Quality Factors of Fruits and Vegetables - American Chemical Society

Chapter 21

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Processing and Storage Influences on the Chemical Composition and Quality of Apple, Pear, and Grape Juice Concentrates Ronald E. Wrolstad, David A. Heatherbell, George A. Spanos, Robert W. Durst, Juinn-Chin Hsu, and Brian M. Yorgey Department of Food Science and Technology, Oregon State University, Corvallis, OR 97331 Apples (Granny Smith), pears (d'Anjou, Bartlett, Comice) and grapes (Thompson Seedless) were processed into juice and juice concentrate and stored at 25ºC. The influences of pear fruit maturity (hard vs. soft) and length of post-harvest storage of apple fruit (3 vs. 9 months) were examined, as were the following processing treatments -addition of SO , and fining with bentonite-gelatin-silica sol. Browning and clarity of the finished products were the quality attributes of primary concern. Detailed compositional analyses (sugar, nonvolatile acid and phenolic profiles, total acidity, total protein, total phenolics, formol values, and gel electrophoresis of proteins) were performed on the 28 samples. SO2 treatment protected phenolics, particularly procyanidins, as well as total soluble proteins. Formol values were better predictors of browning rates during storage (within fruit commodities) than were i n i t i a l browning indices. Fining does not influence browning rates, but is effective in preventing haze formation. 2

Processing apples, pears and grapes into juice concentrate is a means of u t i l i z i n g surplus fruit and defects such as under and oversized f r u i t . This allows for more complete utilization of these agricultural commodities, with economic and ecological benefits to growers, processors and consumers. In addition to being used as single strength juices, there is increasing demand for the use of apple, pear and white grape juice concentrates as ingredients for blended juices, syrups, juice drinks and soft drinks. There are different quality prerequisites for these various end products and there is considerable quality variation among the concentrates available in the commercial marketplace. There is no standard of identity for these concentrates in the USA. In this investigation we processed pears, apples and Thompson seedless grapes into juice and juice concentrate and tracked the compositional changes through processing and storage. The quality 0097-6156/89/0405-0270$06.75/0 c 1989 American Chemical Society

Jen; Quality Factors of Fruits and Vegetables ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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attributes of primary interest were color and appearance, i . e . browning, sedimentation and haze. A major objective was to determine those compositional indices which could be predictive of product quality. We were also interested in finding compositional indices which reveal processing/storage history as well as those which are useful in determining authenticity. This chapter summarizes the r/esults of this study, the original references (1-7) should be referred to for details of experimental methods and complete listings of compositional data. Downloaded by UNIV OF MICHIGAN ANN ARBOR on May 20, 2016 | http://pubs.acs.org Publication Date: September 7, 1989 | doi: 10.1021/bk-1989-0405.ch021

Processing and Storage Trials Figures 1, 2, and 3 outline the unit operations for the different processing t r i a l s . SO2 addition is commonly used in commercial processing of Thompson seedless grapes into concentrates. We were particularly interested in i t s influence on composition and quality and did parallel t r i a l s with and without addition of 70 ppm SO2. All samples were given a prepress commercial pectinase treatment, a procedure which is being used in industry to increase juice yields. Trials with and without fining (addition of Bentonite, gelatin and S i l i c a Sol) were conducted because of the interest in haze and sediment formation. Juices were pasteurized and bottled as single strength, and also concentrated to 71° Brix. Juice and concentrates were stored at 25°C A l l processing t r i a l s were replicated. Those points of processing and storage where samples were collected for compositional analyses were indicated by an asterisk in Figures 1, 2 and 3. Granny Smith was the variety of apples selected for juice processing. The influence of long-term storage of fruit was investigated as apples are commonly held in cold storage for considerable periods of time before processing. Processing t r i a l s were carried out on f r u i t from the same lot which had been stored for three and nine months. A l l apple juice samples were given a prepress treatment with a commercial pectinase preparation. Trials with and without fining were conducted. The protocol for bottling of single-strength juices, concentration and storage regimes were the same as for the grape t r i a l s . Three varieties of pears, Bartlett, Cornice and d'Anjou, were included in this investigation. As commercial processors u t i l i z e both hard, unripe fruit and soft, ripened f r u i t in juice manufacture, the influence of ripening was investigated for a l l three varieites. Juice was pressed from green fruit as well as f r u i t from the same lot which had been ripened by removing from cold storage M ° C ) and holding at 15°C for 5-7 days. The influence of SO2 (50 ppm) addition was included for separate lots of unripe Cornice and d'Anjou f r u i t . Fining was found to be essential for satisfactory f i l t r a t i o n of a l l pear juice samples; therefore, there were no comparative unfined pear juice experimental t r i a l s . Sugar Composition Sucrose, glucose, fructose and sorbitol were separated and quantitated by HPLC. The sample preparation procedure included removal of acids by percolating the juice through a minicolumn


272

QUALITY FACTORS OF FRUITS AND VEGETABLES

^Thompson Seedless Grapes)


Crush and Destem (S0

2

Addition, 70 ppm)

(No SOg Addition)

^Prepress Pectinase Treatment, 50 ppm Rohapect D51.)

,

ι

1

/

* (Press, Willmes Bladder Press with 1% Rice Hulls J

I

• (Enzyme Clarification, 150 ppm Rohapect D5L) I Z Fine 500 ppm Bentonite 100 ppm Gelatin 300 ppm Silica Sol

Bottle Single Strength, 85° C 2 min.

* Samples obtained for analysis

^Fin^^No!Fine)

Concentrate Rot. Evap. -60° C 71° Brix

I I II 9

Store mo., 25° C

Figure 1. Unit operations for processing Thompson Seedless white grape juice samples. (Reproduced from ref. 4. Copyright 1989 American Chemical Society.)


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^Granny Smith AppiesJ


( Short Storage, 3 mo., -1° c ) ^ Long Storage, 9 mo., ~1° c )

(

Grind, Hammer—Mill

1

^

)

L

Γ Prepress Pectinase Treatment, 50 ppm Rohapect D5LJ

I

i

* Γ Press, Hydraulic Rack & Cloth with 1% SilvaCel Press AidJ

I * (

I HTST, 89° C, 90 sec.

I

)

I

Enzyme Clarification, 100 ppm each Rohapect DA1L and HT (NO Fine)

Fine 500 ppm Bentonite 100 ppm Gelatin 300 ppm Silica Sol

c c

Cold Settle Overnight

Filter, 1% DE

Bottle Single Strength, 85° C 2 min.

* Samples obtained for analysis

j

3

Concentrate Rot. Evap. -60° C 69° Brix M

M

Store 9 mo., 25° C

Figure 2. Unit operations for processing Granny Smith apple juice samples. (Reproduced from ref. 2. Copyright 1989 American Chemical Society.)


274


Comice, D'Anjou & Bartlett Unripe Fruit

Cornice & D'Anjou Unripe Fruit

c Downloaded by UNIV OF MICHIGAN ANN ARBOR on May 20, 2016 | http://pubs.acs.org Publication Date: September 7, 1989 | doi: 10.1021/bk-1989-0405.ch021

S0

2

Comice, D'Anjou & Bartlett Ripened Fruit

Spray, -50 ppm

ι

Grind, Hammer Mill i s C ^ Addition, 50 ppmj — j Γ Prepress Pectinase Treatment, 50 ppm Rohapect D5I_) ,

' I I . Press, Hydraulic Rack & Cloth with 1% SilvaCel Press Aid! ,• ^

I

I

I ,

HTST, 89° C, 90 sec.

I

τ

J

* I Enzyme Clarification, 100 ppm each Rohapect DA1L and HT ^SC>2 Adjustment to 30 ppm Free) •• - \

r

Fine 500 ppm Bentonite, 100 ppm Gelatin, 300 ppm Silica Sol ν . )

1

( *(

ι

I

Cold Settle Overnight

1

1 Filter, 1% DE

Bottle Single Strength 85° C, 2 min.

) )

Concentrate, Rot. Evap. -60° C, 69° Brix

, ι ι ι;

* Samples obtained for analysis ^ Store, 9 mo., 25° C j * Figure 3. Unit operations for processing Bartlett, Cornice, and D'Anjou pear juice samples. (Reproduced from ref. 3. Copyright 1989 American Chemical Society.)



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containing anion exchange resin and removing phenolics by treatment with C-18 reverse phase cartridges (JJ. Mannitol was used as an internal standard. Compositional data for a l l pear samples was normalized to 11.0° Brix; apple and grape samples were normalized to 11.5° and 16.5°, respectively. Normalization to a standard °Brix value facilitates comparisons among experimental and commercial samples. Table I summarizes the results for the pear juice samples. There is l i t t l e difference in the °Brix value for juices from unripe and ripened pears. The values for the individual sugars are presented as percent of total sugars (summation of glucose, fructose, sucrose and sorbitol). Fining and SO2 treatment had no influence on the sugar profile. This was true for the apple and grape samples as well Ripening appears to have an influence on sucrose and sorbitol levels. Unripe Bartlett juice had higher levels of sucrose than juice from ripened f r u i t ; the reverse was true for Cornice and d'Anjou, however, with ripe fruit having lower levels of sucrose. Juice from unripe Cornice and d'Anjou pears had higher levels of sorbitol than that from the ripened f r u i t . Chromatograms from a l l fruits showed trace ( Ε 200Ί

Unripe, -S02 Unripe, +S02 Ripe, -S02

nripe, -S02 nripe, +S02 ipe, -S02

ο

CO

>* 50 1 ϋ ο

"c

c

CO

E F,Ft B Treatment

C

CS

D. Procyanidins B Comice (Comice & D'Anjou) gg D'Anjou

â 1 00

Τ

H3 Unripe, -S02 Unripe, +S02 • Ripe, -S02

E F,Ft Β Treatment

Flavonols (Comice)

Figure 7. Effect of processing and storage on the phenolics of pear juice. Unit operations code: P, pressed juice; H , heat treatment; E , enzyme clarification; F, fined; Ft, filtered; B, bottled single-strength juice; C, concentrate; and CS, stored concentrate.

E F, Ft Β Treatment

Arbutin (Cornice

E F,Ft Β Treatment

Cinnamics (D'Anjou)



284


Arbutin, in contrast to the other phenolics, is very stable through storage and a l l processing unit operations (Figure 7C). Its stability along with its limited distribution in other fruits are characteristics that should promote its use as a reference marker for pear. Procyanidins were not detected in pear juice unless they were treated with SO2. Figure 7D compares the procyanidin levels in Cornice and d'Anjou juices through processing and storage. Cornice contained higher amounts of procyanidins than d'Anjou. HTST treatment had a protective effect, the procyanidins being reasonably stable through subsequent processing steps. They completely disappeared, however, after nine months storage as a concentrate. White Grape Pehnolics. The same analytical system was again effective for the phenolic acids, flavonols and procyanidins of Thompson Seedless white grape juice. Grape differs from apple and pear in that the cinnamic acids are esterified with tartaric acid rtaher than quinic acid to give caftaric and coutaric derivatives. Figure 8A shows an HPLC chromatogram of the cinnamic acids and phenolics and Figure 8B shows a chromatogram of the procyanidin fraction. Figure 9A shows the effect of processing and storage on the cinnamics of white grape juice. SO? protected cinnamics from oxidation. (HTST treatment was not done in the grape processing t r i a l s , so its effectiveness in inactivating PPO was not evaluated.) Fining, f i l t e r i n g , bottling and concentration had l i t t l e effect on the cinnamics. There was a substantial loss of cinnamics during long-term storage of the concentrate. The effect of processing and storage on the procyanidins of white grape juice is shown in Figure 9B. The most striking result is the complete disappearance of the procyanidins during long-term storage of the concentrate. SO2 addition had a protective influence on the procyanidins while these compounds were relatively stable to the other processing operations. Haze and Sediment Formation Table III gives the protein content and percent haze readings for the single-strength apple juice and reconstituted apple juice concentrate samples. All of the samples showed high clarity as evidenced by the low haze readings, none having a propensity towards haze or sediment formation. A decrease in total soluble proteins was observed with increased storage time of apple f r u i t . Fining resulted in ca. 25-50% reduction in total soluble protein. Polyacrylamide gel electrophoresis (PAGE) revealed that fining removed low molecular weight (

Quality Factors of Fruits and Vegetables - American Chemical Society

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