Comparison of Aroma-Active Compounds and Sensory Characteristics

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Comparison of Aroma-active Compounds and Sensory Characteristics of Durian (Durio zibethinus L.) Wines Using Strains of Saccharomyces cerevisiae with Odor Activity Values and Partial Least Squares Regression ZUOBING XIAO, Jiancai Zhu, Feng Chen, Lingying Wang, YunWei Niu, Chang Shu, and HeXing Chen J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf505666y • Publication Date (Web): 25 Jan 2015 Downloaded from http://pubs.acs.org on February 2, 2015

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Journal of Agricultural and Food Chemistry

Comparison of Aroma-active Compounds and Sensory Characteristics of Durian (Durio zibethinus L.) Wines Using Strains of Saccharomyces cerevisiae with Odor Activity Values and Partial Least Squares Regression JianCai Zhua, Feng Chena,b, LingYing Wangc, YunWei Niua, Chang Shua, HeXing Chena and ZuoBing Xiaoa* a

Department of Perfume and Aroma Technology, Shanghai Institute of Technology, Shanghai, China

b

Department of Food, Nutrition, and Packaging Sciences, Clemson University, Clemson,

USA 29634 c

Shanghai Cosmax (China) cosmetics co., LTD, Shanghai, China

Corresponding Author *Correspondence author: Xiao Zuobing Address: School of Perfume and Aroma Technology, Shanghai Institute of Technology, 100 Haiquan Road, Shanghai, 201418, People’s Republic of China Tel: 0086-021-60873424 Fax: 0086-021-54487207 Email: [email protected]

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Abstract:

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The study evaluated the effects of five different strains (GRE, RC212, Lalvin

3

D254, CGMCC2.4, and CGMCC2.23) of the yeast Saccharomyces cerevisiae on the

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aromatic characteristics of fermented durian musts. In this work, 38 and 43

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compounds in durian juices and wines were analyzed by gas chromatography-mass

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spectrometry (GC-MS) and GC-pulsed flame photometric detection (GC-PFPD) with

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the aid of stir bar sorptive extraction (SBSE), respectively. According to the measured

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odor activity values (OAV), only 11 and 15 aroma compounds had OAVs greater than

9

1 in juices or durian wines, among which 2,3-butanedione, 3-methylbutanol, dimethyl

10

sulphide, dimethyl disulphide, methyl ethyl disulphide, ethyl 2-methylbutanoate, ethyl

11

butanoate and ethyl octanoate were major contributors to aroma of juices and wines.

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Partial least squares regression (PLSR) was used to detect positive correlations

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between sensory analysis and aroma compounds. The result showed that the attributes

14

were closely related to aroma compounds.

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Keywords: Saccharomyces cerevisiae; Durian wine; Aroma; OAV; PLSR


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Introduction

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The aroma profile is one of the major characteristics that define the differences

18

quality among various fruit wines. The profile is a complex mixture of compounds

19

that are the result of the microbiological conversion of sugars, amino acids, and other

20

chemical components to ethanol, carbon dioxide, and secondary metabolites.1These

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metabolites, along with the intrinsic compounds in the fruit, are responsible for

22

characterisation and differentiation of aroma in fruit wines.

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The fruit wine aroma compounds can be influenced by many factors such as:

24

fruit variety, geography, and growing circumstances, but also depends on yeast strain,

25

and the pH of the medium.2 Although each of these factors exerts an important

26

influence on the quality of the fruit wine, the yeast strain plays a key role in the

27

development of aroma in fruit wines during alcoholic fermentation.

28

Different strains of S. cerevisiae can produce significantly different aroma

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profiles when fermenting the same musts. This is a consequence of the differential

30

ability of wine yeast stains in synthesising yeast-derived volatile compounds.3

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Therefore, the selection of the proper yeast strain can be critical for the development

32

of the desired fruit wine style.

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Durian (Durio zibethinus L.) is a popular and expensive tropical fruit widely

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grown in South-East Asia. Durian is entitled as “King of tropical fruits” due to its

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superlative flesh, which is rich in nutritional components.4 However, some problems

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persist in the processing of durian: on the one hand, durian fruit has an excellent,

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unique flavor, but has a strong, distinctive aroma which makes it difficult to transport

38

and store. On the other hand, the price of durian has declined sharply due to an

39

oversupply of the fruit during the durian season. Thus, attempts have been made to

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add value to the durian fruit crop. One method for solving these problems is turning it



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into fruit juices or wines. According to the reference, 5 tropical fruit juices or wines

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have become popular since an increasing number of people are aware of the health

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benefits of natural fruit juice. Therefore, fruit wines have become alternatives to

44

traditional caffeine-containing beverages such as coffee, tea, or carbonated soft

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drinks.

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Several studies on the aroma fractions of durian showed great variability on 4,6,7

47

concentration of aroma compounds.

Durian fruits possessed two distinct odor

48

notes, i.e. strong sulfur/onion-like, and slight fruit-like.6,7 Moreover, the previous

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study8 demonstrated the impact of nitrogen supplementation on durian wine

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fermentation by Saccharomyces cerevisiae. However, to the best of our knowledge,

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the aroma of durian wine fermented with strains of Saccharomyces and the correlation

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between samples, sensory attributes, and aroma compounds had not yet been

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characterized.

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Therefore, the aims of the present study were: (1) to characterize the aroma

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compounds in durian wine using SBSE followed by capillary GC-MS and GC-PFPD

56

analysis for the first time; (2) to evaluate the influence of different yeast strains of

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Saccharomyces on the analytical and sensory properties of durian wines; (3) to

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establish the relationship between samples, sensory attributes, and aroma compounds

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using multivariate analysis of PLSR. A better understanding of these points will be

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helpful for improving the characteristic aroma of durian wine by adjusting

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fermentation parameters or compensating for typical aroma compounds after alcoholic

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fermentation.

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Materials and methods

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Yeast strains

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Five different commercial yeast (S. cerevisiae) strains were used in this research.


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Strains GRE (Y1), Lalvin RC212 (Y3) and Lalvin D254 (Y4) were supplied by

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Lallemand (France). The result showed that strain GRE was found capable to produce

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high amounts of volatile esters, whilst strains RC212 and D254 showed excellent

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capability in production of alcohol compounds.9 Two strains were isolated from

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Sichuan Province, named CGMCC2.23 (Y2) and CGMCC2.4 (Y5), preserved in

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Northeast Institute of Science.

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Chemicals

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Acetaldehyde,

methanethiol,

ethanethiol,

dimethyl

sulphide,

1-propanol,

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2,3-butanedione, propane-1-thiol, ethyl acetate, 2-butenal, acetic acid, 1-butanol,

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2-pentanone, dimethyl disulphide, methyl propanoate, (Z)-2-but-2-ene-1-thiol, methyl

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butanoate,

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2-methyl-2-butenal, ethyl 2-methylpropanoate, butanoic acid, 2,3-butanediol, ethyl

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butanoate,

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2-methyl-2-pentenal, methyl ethyl disulphide, ethyl 2-butenoate, ethyl thiolacetate,

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ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, diethyl disulphide, propyl

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2-methylbutanoate,

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hexanoate, propyl 2-methyl-2-butenoic acid, ethyl 2-hexenoate, propyl hexanoate,

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ethyl heptanoate, dipropyl disulphide, ethyl 2-methylhexanoate, methyl octanoate,

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3,5-dimethyl-1,2,4-trithiolane, diethyl trisulphide and ethyl octanoate were purchased

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from Sigma-Aldrich (Saint Louis, MO). All of them were analytical reagents.

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Durian musts

3-methylbutanol,

propyl

2-methylbutanol,

propanoate,

3-methylbutyl

butyl

2-octanol

acetate,

propanoate,

(Internal

Standard),

3-methylbut-2-ene-1-thiol,

3-methylthio-1-propanol,

ethyl

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Fresh durian fruits (Durio zibethinus L.) cultivar ‘Monthong’ were purchased

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from Wal-Mart Stores in Shanghai originating in Malaysia. Only fully ripened fruits

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without any split on the husk were selected for the study. 5 kg of durian fruits were

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washed in clean water to remove plant residue. Next, the pulp was extracted manually



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by mechanical pressure. Seeds and pulp residue were separated from the juice by

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centrifugation (RCF=11000, 12 min, 18 °C).

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Then, the musts were pasteurized for 30 min at 65 °C, cooled down and poured

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into 10 L bottles. The initial values of musts were as follows: total sugars 163 g/L, pH

95

6.3. The fruit musts were mixed with a sucrose solution to adjust the total sugars to

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210 g/L. The pH was adjusted to 3.5 with 1 mol/L DL-malic acid. Sulfur dioxide, in

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the form of potassium pyrosulfit, was added into the musts to maintain the

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concentration of 50 mg/L free SO2 to inhibit bacterial growth. All experiments were

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carried out in triplicate.

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Durian wine production

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The fermentation temperature for durian wine production was approximately

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20 °C and no stirring was performed during any stage of the fermentation. Yeast

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strains were grown in YPG medium (1% yeast extracts; 2% peptone and 2% glucose).

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With a platinum loop, yeasts were inoculated into tubes containing 200 mL of YPG

105

broth at 20 °C until the cell density approximately reached up to 107 cells/mL. The

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cells were counted and an equal amount of cells per strain was resuspended in the

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same medium for the fermentation. Each vat was then inoculated with 10 mL prepared

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suspension to obtain the final cell density of 106 cells/mL. 4 L durian musts were

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utilized for durian wine production. All vinifications were carried out in a 10 L

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bioreactor at 20 °C. Fermentation was monitored through measuring viable cells and

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total reducing sugars. The fermentation was considered to be ended when the sugar

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content was below 1 g/L. After fermentation, fermented durian musts were transferred

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to the 10 L bottles and stored at 5 °C for biomass sedimentation. After 24 h, the durian

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wines were transferred to new bottles without aeration. After 10 days, wines were then

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filtered with cellulose filters and stored at 5 °C in sealed glass bottles to avoid oxygen


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entrance.

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Standard chemical analysis

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The official methods of the Office Internationale de Vigne et Vin10were

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employed for the conventional determinations, such as pH, ethanol content, total

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acidity,

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Boehringer-Mannheim (Germany) test kit was used. Yeast growth was followed

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spectrophotometrically (Shimadzu, Kyoto, Japan) by absorbance at 600 nm. Viable

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cells were determined by plating and counting of colonies on YPG agar.

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SBSE adsorption of aroma compounds

free

SO2

and

total

reducing

sugar.

To

analyze

glycerol,

the

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Each wine sample (5 mL) was placed in a 20 mL vial, in which 20 µL of internal

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standard solution (2-octanol, 50 mg/L in the ethanolic solution) were added. A stir bar

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(Twister) coated with poly-dimethylsiloxane (PDMS) phase (1 cm length, 0.5 mm

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thickness, Gerstel Inc., Baltimore, MD) was used to extract the aroma compounds

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from the sample. The Twister bar was constantly stirred for 50 min at a speed of 600

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rpm and 40 ° C for extraction temperature. After sampling, the Twister bar was rinsed

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with distilled water, dried with a Kimwipe tissue paper, and placed into the sample

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holder of the thermal desorption unit (TDU) (Gerstel, Inc.).

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The analyzes were performed using a TDU sampler (Gerstel, Inc., Baltimore,

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MD) mounted on an Agilent GC-MS system (Agilent 7890-5975 GC-MS, Agilent

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Technologies, USA). The analytes were thermally desorbed at the TDU in splitless

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mode, ramping from 45 to 240 ° C at a rate of 5 ° C/min, and held at the final

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temperature for 5 min. The desorbed analytes were cryofocused (-80 °C) in a

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programmed temperature vaporizing (PTV) injector (CIS 4, Gerstel, Inc.) with liquid

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nitrogen. After desorption, the PTV was heated from - 80 to 240 ° C at a rate of 10

140

°C/s and held at 240 ° C for 5 min. The solvent vent injection mode was employed.



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GC-MS identification of aroma compounds

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The analyzes were performed using a Hewlett-Packard 7890 GC with a 5975

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mass selective detector (MSD) (Agilent Technologies, USA) instrument operating

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under electron ionisation (EI) mode (70 eV, ion source temperature 230 °C) with the

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quadrupole in a scanning mode (scan range was m/z 30-450 at a scan rate of 1 scan/s).

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Separation of compounds was achieved on Innowax-Wax (60 m × 0.25 mm i.d. ×

147

0.25µm film thickness, Agilent Technologies, USA) and DB-5 (60 m × 0.25 mm i.d.

148

× 0.25µm film thickness, Agilent Technologies, USA). Helium (purity 99.999%) was

149

used as a carrier with a constant flow velocity of 1 mL/min. The quadrupole mass

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filter was at 150 °C. The transfer line temperature was operated at 250 °C. The oven

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temperature was held at 35 °C for 3 min, then ramped to 60 °C at the rate of 2 °C/ min

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and ramped at the rate of 6 °C/min to 240 °C for the last 5 min. The volatile

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compounds were identified by comparing retention indices and retention times with

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those obtained for authentic standards, or those of literature data, or with mass spectra

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in the Wiley and Nist11 librarys. The RIs were determined via sample injection with a

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homologous series of alkanes (C5-C30) (Sigma-Aldrich, Saint Louis, MO).

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GC-MS quantitation of aroma compounds

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In order to obtain a similar matrix as durian wine, model wine was prepared

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containing 15.0 g/L of malic acid, 0.5 g/L of lactic acid, 2.0 g/L of citric acid, 10.0 g/L

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fructose, 8.0 g/L glucose and 12% of ethanol in Milli-Q deionized water. The pH was

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adjusted to 4.0. Quantitation of the major aroma compounds was carried out by

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standard curves obtained by each compound from six different concentrations in

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ethanol. The levels of the aroma compounds were normalized by 2-octanol

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equivalents. The ethanolic solution of internal standard 2-octanol (20 µL of 50 mg/L)

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was introduced to the 5 mL of model wine in a 20 mL vial then extracted by SBSE, as


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was performed for the durian wines.

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The standard curves were showed in the research, where ‘‘y” represented the

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peak area ratio (peak area of volatile standard/ peak area of internal standard) and ‘‘x”

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represented the concentration ratio (concentration of volatile standard/concentration

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of internal standard). The calibration curves were obtained from chemstation software

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(Agilent Technologies Inc.) and used for calculation of volatiles in juices and durian

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wines.

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Gas chromatography-PFPD

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HP-5890 Series II GC from Agilent (Santa Clara, CA) equipped with a 5380

175

PFPD detector from OI Analytical (College Station, TX) was used in the sulfur mode.

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Separation of compounds was achieved on Innowax-Wax (60 m × 0.25 mm i.d. ×

177

0.25 µm film thickness, Agilent Technologies, USA) and DB-5 (60 m × 0.25 mm i.d.

178

× 0.25 µm film thickness, Agilent Technologies, USA). The oven temperature was

179

held at 35 °C for 3 min, then ramped to 60 °C at the rate of 2 °C/ min and ramped at

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the rate of 6 °C/min to 240 °C for the last 5 min. GC was operated in a constant flow

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mode (1 mL/min) with helium as the carrier gas. PFPD detector was set at 250 °C and

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PMT voltage was set at 500 V. The sulfur-containing compounds were confirmed by

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comparison with authentic standards on both columns and RI value matching. The

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quantitation method was identical to the GC-MS analysis as described in the above

185

section. The samples were run in triplicate.

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Sensory analysis

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A quantitative descriptive sensory analysis was applied for evaluating 5 fruit

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wine samples using a 18 cm line scale by a well-trained panel consisted of 20

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members (10 females and 10 male, age: 20-30). Before the quantitative descriptive

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analysis, 30 mL of fruit wine was put in a 100 mL volume of white china cup covered



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with a plastic Petri dish and was served to a panelist in laboratory at a room

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temperature (25 °C). And 20 judges had discussed aroma compositions of samples

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through three preliminary sessions (each needs 3 h), until everyone agreed to use them

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as the attributes. Then, the quantitative descriptive analysis was executed using five

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sensory attributes (fruity, sulfur, sweety, off-flavor and harmony) for all five samples

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that were randomly divided into two sessions. In every session, samples were

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randomly presented for every member to avert causing a so-called order effect. All of

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the samples were evaluated in triplicate.

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Odor activity values (OAV)

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The contribution of each odor to the overall fruit wine aroma was evaluated by

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the odor activity value, which was measured as the ratio of the concentration of each

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compound to its detection threshold. The threshold values were taken from

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information available in the references (shown in Table 3).

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Statistical analysis

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The chemical data and quantitative descriptive sensory analysis were submitted

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to variance analysis (ANOVA). Duncan’s multiple comparison tests were applied to

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determine significant differences between the samples and sensory attributes. All the

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analysis was carried out employing the XLSTAT ver.7.5 (Addinsoft, New York, NY,

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USA).

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Partial least squares regression (PLSR) was employed to explore the correlations

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between samples, aroma compounds and sensory attributes using the Unscrambler

212

version 9.7 (CAMO ASA, Oslo, Norway). All variables were centered and

213

standardized (1/Sdev) so as to make each variable have a unit variance and zero mean

214

before applying PLS analyzes finally obtain unbiased contribution of each variable to

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the criterion. All PLSR models were validated using full cross-validation.


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Results and discussion

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Micro-vinifications

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The five S. cerevisiae (Y1, Y2, Y3, Y4, and Y5) commercial fruit wine yeast

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strains showed growth indication when incubated at 20 °C (Fig. 1). Fermentation

220

parameters were calculated for these strains. Among the five strains, the growth rate

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of strain Y1 was higher than that of the other strains and the cell density reached

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6.4 × 107 cells/mL on Day 6 of growth (Fig. 1A). Then the viability decreased and

223

viability loss was measured at 25.8 % after Day 8 in culture Y1. Strains Y3 and Y5

224

presented a cell density increase in the first 4 days of incubation and reached their

225

maximum cell density of 5.1 × 107 cells/mL and 4.9 × 107 cells/mL respectively:

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thereafter it remained almost constant at a cell density of 1 × 107 cells/mL. Strain Y4

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had a 2-day adaptation period (lag phase) and then started to grow at a slower rate

228

than the other strains. Although strain Y4 showed delayed growth, it remained a strain

229

with a rapid growth rate overall.

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The sugar values in five S. cerevisiae strains displayed similar patterns of rapid

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initial reduction (Fig. 1B). Strains Y1, Y2, and Y5 showed a gradual reduction in

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sugar value over the 10-day fermentation period and reached a stable sugar level

233

around 1.1 to 1.2 g/L, indicating that almost all of the sugars were consumed and that

234

the fermentation process was considered to have ended. Both strains Y3 and Y4

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showed the similar behavior, i.e. a 14-day fermentation period was noted.

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Different strains of S. cerevisiae showed significantly different growth rates and

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differential ability in metabolising sugars as a result of their biochemical mechanisms

238

and metabolic activity during alcoholic fermentation. Furthermore, it had been

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suggested that differences in the genes of S. cerevisiae strains play a central role in

240

explaining the diversity of aroma profiles produced by each different strain.11



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Therefore, the choice of the proper yeast strain could be critical for the development

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of the desired flavor and aroma of such fruit wines.

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Table 1 presents the values of each major parameter (mean ± standard deviation,

244

n = 3) of durian wines fermented with the five yeast strains. The statistical analysis

245

demonstrated that the yeast strains showed significant differences in the values of

246

important parameters, such as the value of: pH, total acidity, reducing sugar, free SO2,

247

and glycerol. The alcohol content of the fruit wines varied a little between 11.2% and

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11.5% (v/v): the highest content was measured in a fruit wine fermented with strain

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Y5 and the lowest content in that produced by strain Y1. However, based on Duncan’s

250

multiple comparison tests, the fruit wines fermented with those two strains showed no

251

significant difference in alcohol content. The highest concentration (17.8 mg/L) of

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free SO2 was found in the Y5-derived fruit wine and the lowest concentration (13.8

253

mg/L) was detected in the Y3-derived fruit wine. As shown in Table 1, the fruit wine

254

fermented with strain Y1 presented the lowest concentration of reducing sugars of

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0.64 g/L. The results indicated that strain Y1 possessed the highest capability to

256

ferment reducing sugar.

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Strain Y3 was an efficient producer of glycerol (1.6 g/L), which was produced

258

from dihydroxyacetone phosphate in the initial fermentation stage. In this stage, the

259

excessive NADH generated during biomass formation would be converted into NAD+

260

by the yeast cells.

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the most important fermentation product and it was considered to contribute positively

262

to the sensory quality of fruit wine. 12, 13

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Identification of volatile compounds in durian juices and wines

12

Besides ethanol and carbon dioxide, glycerol was quantitatively

264

SBSE with GC-MS and GC-PFPD was applied for the first time in the analysis

265

of the aroma fraction of durian juices and wines. The main parameters that were


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known to influence the methodology were investigated, such as extraction time,

267

extraction temperature, and sample volume. According to the results obtained (data

268

not shown), optimized SBSE experimental conditions were established, i.e. 50 min of

269

extraction time, 40 °C extraction temperature, and a sample volume of 5 mL.

270

In the present work, 38 and 43 aroma compounds in durian juices and wines were

271

analyzed by GC-MS and GC-PFPD with the aid of SBSE, respectively. The aroma

272

compounds with higher concentration detected in the juice included alcohols

273

(1-propanol, 2,3-butanediol and 3-methylbutanol), esters (ethyl acetate and methyl

274

propanoate) and sulfur-containing compounds (dimethyl sulphide, dimethyl

275

disulphide, methyl ethyl disulphide and diethyl disulphide). Compared with the juice,

276

the content of compounds such as ethyl octanoate, ethyl 2-hexenonate, ethyl

277

hexanoate, and ethyl 2-methylbutanoate predominated in durian wines.

278

Among the aroma compounds present in fruit wine, only a sub-set was sensorily

279

detectable. Thus, to evaluate the influence of compounds on the formation of aroma

280

characteristics of durian wines, the selection of specific compounds from GC analysis

281

to represent the attributes in samples might be useful. As reported by previous

282

literature14, the low concentrations of several fermentative aroma compounds could

283

not actually reflect the influence on the perceived aroma intensity in samples due to

284

their low detection thresholds. This phenomenon was particularly evident in tropical

285

fruits. Therefore, the odor activity value (OAV) was usually used to provide a rough

286

evaluation of the real contribution of each aroma compound to the global aroma.15

287

According to the previous literature16, compounds with OAVs > 1 were commonly at

288

the perception level and considered important aroma compounds contributing to fruit

289

wine aroma.

290

According to OAVs (Table 3), only 11 and 15 aroma compounds were analyzed



291

with the OAVs greater than 1 in juice or durian wines: dimethyl sulphide,

292

2,3-butanedione, ethyl acetate, dimethyl disulphide, ethyl propanoate, methyl

293

butanoate, 3-methylbutanol, ethyl 2-methylpropanoate, ethyl butanoate, propyl

294

propanoate, methyl ethyl disulphide, ethyl 2-methylbutanoate, diethyl disulphide,

295

3-methylbutyl propanoate, ethyl hexanoate, 3,5-dimethyl-1,2,4-trithiolane and ethyl

296

octanoate. Amongst these compounds, 2,3-butanedione, 3-methylbutanol, dimethyl

297

sulphide, dimethyl disulphide, methyl ethyl disulphide, ethyl 2-methylbutanoate, ethyl

298

butanoate and ethyl octanoate were major contributors to aroma of juices and wines.

299

3-Methylbutanol, which was responsible for vinous, herbaceous and cacao aroma,

300

is formed during fermentation by deamination and decarboxylation reactions from

301

isoleucine. 17 Compared to five durian wines, the concentration (30.734 mg/L) of this

302

compound only surpassed odor threshold (30 mg/L) in durian juice. In other words,

303

this compound decreased with the progress of fermentation. Obviously, the conclusion

304

was in contradiction with other literature. 17 The reason might be that 3-methylbutanol

305

was consumed by esterification reaction. Correspondingly, the concentration of ethyl

306

3-methylbutanoate increased during the fermentation process.

307

Ester compounds were responsible for the fruity aroma in fruit juice and wines,

308

in particular, those compounds were correlated with the freshness and fruitiness of

309

new wines.13 These compounds in fruit wines were mainly synthesized from their

310

corresponding precursors by enzymatic ethanolysis with the aid of Acyl-CoA during

311

yeast fermentation. Their concentrations were influenced by many parameters, such as

312

yeast strain, fermentation temperature, degree of aeration, sugar content, etc. 18

313

On the one hand, propyl propanoate, ethyl 2-butenoate, ethyl 2-methylhexanoate,

314

3-methylbutyl propanoate, propyl 2-methyl-2-butenoic acid, ethyl 2-methylhexanoate

315

and propyl hexanote were only detected in the fermented wines. The phenomenon


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316

demonstrated that the function of yeasts in the production of aroma was to synthesize

317

yeast-derived aroma compounds during fermentation. On the other hand, as shown in

318

Table 3, ethyl 2-methylbutanoate presented highest value of OAVs, which ranged

319

from 14.603 to 171.807 in juice and five durian wines. As a result, this compound

320

contributed to the juice and wines with banana and pear aroma. 17 Another important

321

ester compound was ethyl octanoate, which was far above its threshold in durian

322

wines, indicating that this compound was a significant contributor to fruity aroma of

323

durian wines. Ethyl octanoate showed its highest OAV (25.749) in Y1-derived durian

324

wine.

325

2-methylbutanoate and ethyl octanoate were synthesized during the fermentation

326

process. Moreover, strain Y1 led to durian wines with the highest OAVs of ester

327

compounds, suggested that Y1 strain possessed a relatively higher ability for ester

328

synthesis.

From

the

above

mentioned,

major

aroma

compounds

like

ethyl

329

Five sulfur-containing aroma compounds were identified across the range of

330

durian wines analyzed, including dimethyl sulphide, dimethyl disulphide, methyl

331

ethyl disulphide, diethyl disulphide, and 3,5-dimethyl-1,2,4-trithiolane. Most of those

332

compounds (dimethyl sulphide, dimethyl disulphide and diethyl disulphide) decreased

333

rapidly with the progress of fermentation. The reduction of sulfur-containing

334

compounds varied with fermentations where strain Y1 had the slowest reduction,

335

followed by strain Y4 and Y5. The result was according with the findings of literature,

336

which showed that most of sulfur-containing compounds might be consumed or

337

degraded to other compounds during the fermentation.19

338

Despite the fact that some sulfur aroma compounds were present in only low

339

relative concentrations, as in the case of dimethyl sulphide and diethyl disulphide in

340

this study, these compounds contributed strong onion-like odor to the fruit wines due



Page 16 of 34

341

to its extremely low threshold, 0.027 µg/L, 0.0043 µg/L, respectively. As reported by

342

previous references, 7,20 the sulfur aroma compounds found in this study might serve

343

as character-impact compounds in durian that contributed to its sulfur note. Dimethyl

344

sulphide was considered as a beneficial compound in low concentrations. The

345

formation of dimethyl sulfide in juice and wine existed not only from its fruit and fruit

346

wine maturation but also during fermentation, which had also variously been linked to

347

cysteine, cystine or glutathione metabolism in yeast. 18

348

What was worth mentioning was that 3,5-dimethyl-1,2,4-trithiolane seemed

349

significant contribution to the durian wine, but it was likely an artificial compound

350

formed during desorption process with the method of SBSE.21-23 Thus, the compound

351

3,5-dimethyl-1,2,4-trithiolane had been excluded as aroma-active compound in the

352

juices and wines.

353

From

the

Table

2,

methanethiol,

ethanethiol,

propanethiol,

and

354

(2Z)-but-2-ene-1-thiol were only present in juices. Although the concentrations of

355

these compounds were relatively low, the contribution to the aroma of the juice might

356

be great due to the low threshold. The result was consistent with the findings of

357

literature19, which showed that these sulfur-containing compounds presented a

358

significant contribution to durian juice aroma. The reason that these compounds were

359

absent from fermented durian wines might be the result of strong volatilisation or

360

utilisation by the yeast strains.

361

Although sulfur compounds were character-impact compounds for durian fruit,

362

these compounds usually perceived as offensive due to the unpleasant aroma.7, 18 On

363

the one hand, it was well known that the quality and value of fruit wines was strongly

364

related to the characteristic aroma profile developed during fermentation process,

365

which contributed to the strengthening of its characteristic organoleptic aroma. On the


Page 17 of 34


366

other hand, there was no doubt that the off-flavor compounds should be controlled in

367

the fermentation process. Therefore, the balance between characteristic aroma and

368

off-flavor attribute was the key to the durian fermentation.

369

Sensory analysis

370

Sensory analysis was performed by the evaluation of the organoleptic qualities

371

of durian wines fermented by the different S. cerevisiae strains, using five

372

descriptors including: fruity, sulfur, sweety, off-flavor, and harmony for their aromas.

373

ANOVA was used to distinguish different durian wines by their sensory evaluation

374

scores. The statistical analysis demonstrated that samples fermented by yeast strains

375

showed significant differences in all attributes, which indicated that these fruit wines

376

had different aroma intensities (p < 0.001).

377

Although judges exhibited significant subjectivity in their use of fruity, sulfur,

378

sweety, off-flavor, and harmony as attribute descriptors, this result was inevitable in

379

such a quantitative descriptive analysis. The reason might be because the judges

380

expressed their perceptions against different scoring criteria, due to their differences

381

in age, background, and olfactory sensitivity. From the research, no significant

382

interaction between judger and replication was found, indicating that all of the judges

383

were reproducible with regard to the scoring of all attributes in triplicate. Similarly,

384

there was no significant interaction between sample and replication (in any attribute).

385

However, according to the statistical analysis, the interaction between sample

386

and judger showed significant differences for the “fruity” (p < 0.01), “sulfur” (p

387

< 0.001), “off-flavor” (p < 0.01), “sweety” (p < 0.01) and “harmony” (p < 0.001)

388

attributes. This result suggested that the judges were scoring samples not consistent

389

with each attribute.

390

Sensory analysis highlighted that some descriptors were statistically influenced



Page 18 of 34

391

by yeast starters (Fig. 2). The durian wines fermented by strains Y1 and Y3 were

392

accompanied by fruity notes more than in other strains. This phenomenon indicated

393

that strains Y1 and Y3 yielded the highest content of compounds able to influence the

394

fruity aroma of the corresponding fruit wine. It was common knowledge that the

395

fruity attribute was the fundamental part of the overall perception of the aroma of

396

durian wine. Therefore, the fruity attribute was an important symbol of fruit wine

397

quality. The durian wines fermented by strains Y1 and Y2 were mostly associated

398

with a greater sweety attribute than wines produced by other strains. The fruit wines

399

fermented by strains Y2 and Y3 were rated as having the highest values of sulfur

400

aroma, whilst durian wine produced by strain Y1 presented low sensorial scores for

401

sulfur aroma. Traditionally, this sulfur aroma was typically associated with a negative

402

sensory contribution to fruit wine (5). 7However, the sulfur attribute remained the

403

characteristic aroma of tropical fruit, which could obviously be distinguished from

404

other fruit by this specific property. In addition, similar behavior was observed for the

405

off-flavor attribute in five fruit wines. The reason might be that sulfur-containing

406

aroma compounds were typically perceived as offensive, they had very low detection

407

thresholds, and generally conferred a negative sensory contribution to fruit wine.

408

The result was consistent with the findings of literature,24 which showed that the

409

sulfur-containing aroma compounds were the main source of off-flavor attributes in

410

fruit wines. The highest score under the harmony attribute was found in fruit wine

411

produced by strain Y1, while the lowest score was found in that produced by strain Y5.

412

Interestingly, by comparing the sensory analysis of harmony and off-flavor attributes,

413

we found that these two attributes presented completely opposite scores when

414

evaluated by our judges.

415

Relationship between samples, aroma compounds, and sensory attributes


7,18

Page 19 of 34


416

PLSR was used to process the mean data accumulated from sensory evaluation

417

by the judges, aroma compounds (OAVs > 1) and samples. The X-matrix was

418

designated as representing the aroma compounds of fruit wines: the Y-matrix was

419

designated as representing the sensory variables and fruit wine samples. The derived

420

PLSR model included two significant PCs explaining 83% of the cross-validated

421

variance (Fig. 3). The result demonstrated that the optimal number of components in

422

the PLSR model presented was determined as two principal components (PC2): the

423

issue of PC2 versus PC3 results was not presented here, as no additional information

424

was gained by its examination.

425

The estimated regression coefficients from the jack-knife uncertainty test showed

426

that all of the aroma compounds, except 3-methylbutanol (C7) and ethyl

427

3-methylpropanoate (C8), were significant for one or more of the five samples and

428

five significant sensory descriptors. Five of the sensory attributes were placed

429

between the inner and outer ellipses, R2 = 0.5 and 1.0, respectively. The result

430

indicated that they were well explained by the PLSR model.

431

From Fig. 3, samples appeared to be divided into three groups according to

432

strain. Among these samples, the fruit wine fermented by strain Y1 was located on the

433

positive region of PC1 and the negative region of PC2. The fruit wines produced by

434

strains Y4 and Y5, which were located on the negative region of PC1 and PC2, were

435

clearly differentiated from samples fermented by other strains. The wines fermented

436

by strains Y2 and Y3 lay in upper part of PC2.

437

The first PC was mainly defined by the aroma descriptors showing a contrast

438

between fruity, harmony, and sweety attributes on the positive dimension, and sulfur,

439

and off-flavor attributes on the negative dimension. The fruit wines produced by

440

strains Y4 and Y5 were negatively correlated to all of the sensory variables and all



Page 20 of 34

441

aroma compounds even though they showed a certain aroma profile in the judges’

442

evaluations thereof. This phenomenon might have been caused by sensory evaluation

443

error, or it might be that those fruit wines could not possess characteristic, or

444

distinguishing, aromas marking them apart from other fruit wines.

445

As compared with other wines, fruit wine fermented by strain Y1 was highly

446

correlated with the sensory attributes of fruity, harmony, and sweety. This was related

447

to aroma compounds, such as: 2,3-butanedione (C2), ethyl acetate (C3), ethyl

448

propanoate

449

2-methylbutanoate (C12), and ethyl octanoate (C16). This phenomenon indicated that

450

strain Y1 should have a higher ethyl acetate yield ability. As reported by literature,

451

2

452

while many fruit-derived compounds were released or modified by the action of

453

aroma-active yeast, and a further substantial portion of fruit wine aroma substances

454

resulted from the metabolic activities of these fruit wine microbes.

455

selection of yeasts was central to the development of fruit wine aroma.

(C5),

methyl

butanoate

(C6),

ethyl

butanoate

(C9),

ethyl

some aroma compounds directly derived from chemical components of the musts,

25

Therefore, the

456

In contrast, sulfur and off-flavor attributes were strongly correlated with each

457

other and showed high loadings in the opposite direction from other attributes. These

458

attributes, which were pronounced in fruit wines fermented by strains Y2 and Y3,

459

were strongly connected with the following compounds: dimethyl sulphide (C1),

460

dimthyl disulphide (C4), methyl ethyl disulphide (C11) and diethyl disulphide (C13).

461

Author information

462

Corresponding Author

463

Correspondence should be addressed to Prof. Xiao Zuobing at the following

464

address, phone and fax number, and email address. Address: School of Perfume and

465

Aroma Technology, Shanghai Institute of Technology, 100 Haiquan Road, Shanghai,


Page 21 of 34


466

200233, People’s Republic of China

467

Tel: 0086-021-60873424

468

Fax: 0086-021-54487207

469

Email: [email protected]

470

Acknowledgments

471

This research was funded by the Natural Science Foundation of Shanghai Institute

472

of Technology [grant number YYY-11607]; the National Natural Science Foundation

473

of China [grant number 21476140], [grant number 21306114]; ‘Twelfth Five Year’

474

National Science and Technology Support Program Topic [grant number

475

2011BAD23B01].

476

Abbreviations used

477

GC-MS,

gas

chromatography-mass spectrometry;

PFPD,

pulsed flame

478

photometric detection; SBSE, stir bar sorptive extraction; OAV, odor activity value;

479

PLSR, partial least squares regression; PDMS, poly-dimethylsiloxane; TDU, thermal

480

desorption unit; PTV, programmed temperature vaporizing.

481



482

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484

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saturnus. LWT - Food Sci Technol. 2012, 46, 84-90.

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Conf. 2013, 13, 9-11.

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compound 3-mercapto-2-methylpentan-1-ol in raw and processed onions (Allium

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dilution assay. J. Agric. Food Chem. 2004, 52, 2797-2802.

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young red wines from different grape varieties. J. Sci. Food Agric. 2000, 80,

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(26) Giri, A.; Osako, K.; Okamoto, A.; Ohshima, T. Olfactometric characterization of

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aroma active compounds in fermented fish paste in comparison with fish sauce,

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fermented soy paste and sauce products. Food Res. Int. 2010, 43, 1027-1040.


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(27) Näf, R.; Velluz, A. Sulfur compounds and some uncommon esters in durian (Durio zibethinus Murr.). Flavor Frag J. 1996, 11, 295-303. (28) Gemert, L. J. v. Complilations of odour threshold values in air, water and other media. Van Setten Kwadraat, Houten, The Netherlands. 2003.



561

Figure captions

562 563 564 565 566 567 568 569 570 571 572 573 574

Figure 1. Evolution of yeasts (A) (as viable cell counts) and total reducing sugar (B) in durian wine during fermentation. Figure 2. Quantitative descriptive analysis of durian wines produced by five yeast strains of Saccharomyces cerevisiae. In sensorial parameters indicated by (***) a difference among some trials is verified for p < 0.001. Figure 3. An overview of the variation found in the mean data from partial least squares regression (PLSR) correlation loading plot for five samples. The model was derived from aroma compounds (OAV > 1) as the X-matrix and samples and sensory variables as the Y-matrix. The concentric circles represent R2 = 0.5 and 1.0, respectively.


Page 26 of 34

Page 27 of 34


Table 1 Mean (n = 3) of general parameters of wines fermented by five different yeast strains.

A

Y1

Y2

Y3

Y4

Y5

pH

3.95±0.01abA

4.08±0.01a

3.87±0.02b

4.01±0.01ab

3.89±0.01b

Ethanol content (% vol)

11.2±0.1a

11.3±0.2a

11.4±0.1a

11.5±0.2a

11.6±0.1a

Total acidity (g/L )

6.2±0.1a

5.9±0.2ab

5.4±0.2b

5.7±0.1ab

5.8±0.1ab

Free SO2 (mg/L)

14.2±0.3b

17.5±0.2b

13.8±0.4b

17.3±0.3a

17.8±0.2a

Glycerol (g/L)

1.4±0.1b

1.5±0.2a

1.6±0.2a

1.3±0.1c

1.1±0.3d

Reducing sugar (g/L)

0.64±0.04c

0.76±0.08b

0.81 ±0.11ab

0.91 ±0.12a

0.82 ±0.09ab

Values with different superscript roman letters (a–d) in the same row are significantly different according to the Duncan test (p < 0.05).



Page 28 of 34

Table 2 Average values (mean ± standard deviation) (mg/L), identification of volatile compounds detected in durian juices and wines fermented by five different yeast strains. RIB CodeA

Juices

Y1

IndentificationC

Compound DB-5

Innowax

Average

SD

D

Average

Y2 SD

1.073

Average

714

MS, RI, Sta

2.700

0.351

24.250

700

PFPD, RI, Sta

0.006

0.001

nd

3

ethanethiol

508

722

PFPD, RI, Sta

0.003

0.000

nd

4

dimethyl sulphide

521

716

PFPD, RI, Sta

1.688

0.101

0.261

0.029

0.822

0.090

0.705

0.048

0.411

0.046

0.599

0.055

5

1-propanol

540

1045

MS, RI, Sta

81.019

5.671

49.122

4.519

33.290

3.063

33.233

3.549

22.559

2.407

49.039

5.885

6

2,3-butanedione

602

970

MS, RI, Sta

1.502

0.180

1.149

0.138

0.914

0.110

0.867

0.090

0.473

0.041

0.677

0.088

7

propane-1-thiol

607

861

PFPD, RI, Sta

0.003

0.000

nd

8

ethyl acetate

608

907

MS, RI, Sta

14.212

1.307

39.626

3.447

13.264

1.154

23.603

9

2-butenal

632

1047

MS, RI, Sta

nd

0.032

0.003

0.017

0.002

nd

10

acetic acid

642

1451

MS, RI, Sta

2.396

0.477

0.042

0.211

0.018

0.265

0.028

0.186

0.018

0.211

11

1-butanol

680

1160

MS, RI, Sta

nd

0.020

0.002

0.021

0.002

0.020

0.002

12

2-pentanone

688

983

MS, RI, Sta

5.501

0.539

5.545

0.479

3.816

0.377

3.566

0.225

13

dimethyl disulphide

710

1071

PFPD, RI, Sta

1.551

0.135

0.337

0.021

1.323

0.083

1.103

0.104

0.387

0.034

0.644

0.072

14

methyl propanoate

721

920

MS, RI, Sta

13.902

1.283

110.439

12.369

79.579

8.913

53.122

4.678

78.388

4.642

12.621

1.300

15

(Z)-2-but-2-ene-1-thiol

722

965

PFPD, RI, Sta

0.033

0.003

nd

16

methyl butanoate

728

1036

MS, RI, Sta

0.371

0.023

1.747

0.140

1.768

0.141

0.879

0.093

0.637

0.058

0.154

0.011

17

3-methylbutanol

746

1252

MS, RI, Sta

30.734

3.442

1.628

0.121

15.612

1.160

4.862

0.481

10.598

0.704

2.445

0.204

0.386

0.388

nd

nd

6.299

0.518

nd

18

2-methylbutanol

749

1210

MS, RI, Sta

7.597

0.782

2.035

0.170

4.632

19

2-methyl-2-butenal

756

1102

MS, RI, Sta

10.584

0.847

6.795

0.565

nd

20

ethyl 2-methylpropanoate

762

955

MS, RI, Sta

0.873

0.065

2.510

0.301

1.158

21

butanoic acid

784

1619

MS, RI, Sta

2.147

0.179

0.167

0.013

22

2,3-butanediol

800

1581

MS, RI, Sta

42.078

3.501

23.513

23

ethyl butanoate

807

1042

MS, RI, Sta

7.452

0.596

24

propyl propanoate

812

1160

MS, RI, Sta

nd

25

butyl acetate

817

1075

MS, RI, Sta

4.754

26

3-methylbut-2-ene-1-thiol

819

1096

PFPD, RI, Sta

27

2-methyl-2-pentenal

830

1108

MS, RI, Sta

nd

nd 2.672

12.640

nd 1.990

nd

nd

4.231

0.301

5.872

0.424

nd

0.101

3.697

0.274

1.697

0.161

0.016

0.197

0.015

1.411

15.448

1.347

15.961

30.764

2.153

12.188

1.125

10.003

1.200

7.582

0.333

19.400

2.134

0.008

0.001

0.002

1.552

0.171

6.857

10.726

1.051

nd

nd

6.879

0.538

nd

nd

nd

nd 0.715

nd

7.681

SD

500

nd

1.184

Average

1) for the main volatile compounds in durian juices and wines fermented by five different yeast strains.

A

ID A

Juices

Y1

Y2

Y3

Y4

Y5

62.520

9.680

30.440

26.120

15.240

22.200

Cooked cabbage, onion,corn

15.018

11.488

9.140

8.665

4.734

6.767

Creamy, sweety,caramel, butter scotch

7.925

2.653

4.721

2.528

2.145

Fruity, buttery, orange

51.705

11.220

44.086

36.759

12.895

21.478

Cooked cabbage, onion

1.636

12.993

9.362

6.250

9.222

1.485

Fruity odor reminiscent of rum

27,28

3.715

17.466

17.679

8.790

6.371

1.542

Apple-like odor

Code

Compound

Oth(mg/L)

C1

dimethyl sulphide

0.027

18

C2

2,3-butanedione

0.1

26

C3

ethyl acetate

5

26

2.842

C4

dimethyl disulphide

0.03

26

C5

methyl propanoate

8.5

27,28

C6

methyl butanoate

0.1

Descripors

C7

3-methylbutanol

30

27,28

1.024

0.054

0.520

0.162

0.353

0.082

Herbaceous and cacao

C8

ethyl 2-methylpropanoate

0.2

26

4.367

12.549

5.792

18.486

8.484

10.578

Strawberry, fruity, sweet

C9

ethyl butanoate

1

26

7.452

30.764

12.188

17.060

9.834

4.888

Fruity, papaya, butter, sweetish, apple, perfumed

C10

propyl propanoate

0.23

26

-

43.490

32.965

35.611

10.038

9.940

C11

methyl ethyl disulphide

0.062

7

46.068

32.198

197.434

143.174

67.029

109.679

C12

ethyl 2-methylbutanoate

0.2

26

14.603

171.807

92.744

109.837

72.865

46.171

Sweet caramel, grape

C13

diethyl disulphide

0.0043

18

106.192

14.011

69.811

55.062

18.682

41.543

Sulfury, roasty, cabbage-like odor

C14

3-methylbutyl propanoate

0.23

27,28

-

11.598

6.995

9.145

6.946

5.892

Pineapple-apricot like odor

C15

ethyl hexanoate

2.3

26

1.637

21.653

13.201

19.783

6.620

4.426

Fruity, green apple

C16

ethyl octanoate

2

27,28

1.500

25.749

18.673

20.311

17.526

7.567

Sulfury, heavy, cocoa odor

Code representing the reference number.


Complex fruity odor reminiscent of apple banana Cooked cabbage, sulfur,onion

Page 31 of 34


A

70

6

B

240

Y1 Y2

60

Y3 Y4

50

Y5

40 30 20

Y1

Total reducing sugar(%)

Number of viable cells/ml(10* )

80

200

Y2 Y3

160

Y4 Y5

120 80 40

10 0

0

0

0

2

4

6

8

10

12

14

2

4

16

6

8

10

12

14

16

Time(days)

Time(days)

Figure 1. Evolution of yeasts (A) (as viable cell counts) and total reducing sugar (B) in durian wine during fermentation.



Figure 2. Quantitative descriptive analysis of durian wines produced by five yeast strains of Saccharomyces cerevisiae. In sensorial parameters indicated by (***) a difference among some trials is verified for p < 0.001.


Page 32 of 34

Page 33 of 34


Figure 3. An overview of the variation found in the mean data from partial least squares regression (PLSR) correlation loading plot for five samples. The model was derived from aroma compounds (OAV > 1) as the X-matrix and samples and sensory variables as the Y-matrix. The concentric circles represent R2 = 0.5 and 1.0, respectively.



TOC Graphic


Page 34 of 34

Comparison of Aroma-Active Compounds and Sensory Characteristics

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