Quality Factors of Fruits and Vegetables - American Chemical Society

Chapter 23

Chemical Changes in Aseptically Processed Kiwi Fruit Nectars B. S. Luh

Downloaded by UNIV LAVAL on April 11, 2016 | http://pubs.acs.org Publication Date: September 7, 1989 | doi: 10.1021/bk-1989-0405.ch023

Department of Food Science and Technology, University of California, Davis, CA 95616 Changes i n chemical constituents of k i w i f r u i t ( A c t i nidia chinensis, Blanch, Hayward c u l t i v a r ) during post-harvest cold storage and ripening under con t r o l l e d conditions were investigated. The f r u i t was harvested at the mature green stage with soluble s o l i d content at 8.0° Brix. Ripening the f r u i t at 20°C under a stream of water-vapor saturated a i r containing 5 ppm ethylene gas resulted i n rapid softening i n texture and r i s i n g of soluble solids to 14.5° Brix i n 4 to 5 days. The increase i n soluble solids was accompanied by increase i n fructose, glucose and decrease i n starch content. The v o l a t i l e compounds i n ripe k i w i f r u i t were i d e n t i f i e d by the gas chromatography-mass spectroscopic methods (GCMS). K i w i f r u i t ( A c t i n i d i a chinensis) i s becoming an important f r u i t crop in C a l i f o r n i a . In 1987, more than 30,000 tons of k i w i f r u i t were produced i n the State. About 20% of the crop are not suitable f o r marketing as fresh f r u i t because of the irregular shape, odd s i z e , defects and soft texture. I t becomes very important to find methods f o r preservation and u t i l i z a t i o n of the crop. One of the approaches i s to process the k i w i f r u i t into juice and nectar. The f r u i t j u i c e industry i s undergoing a period of rapid change i n the technology used f o r processing and packaging of shelf-stable j u i c e s . The change i n technology started i n 1981 with the approval by the Food and Drug Administration (FDA) of hydrogen peroxide f o r the s t e r i l i z a t i o n of packaging materials used i n aseptic processing systems. Since that time, f l e x i b l e multilayer cartons are p a r t i a l l y replacing the t r a d i t i o n a l can and glass con tainers. Presently, increasing amount of apple, c i t r u s , cran berry, pineapple and mixed f r u i t j i c e s are processed by the aseptic packaging tehnique i n 250 mL containers as single-serving juice products (1). The advantages of the high-temperature short-time aseptic canning process on quality retention i n heat-processed products have been discussed by Luh and York (2). The importance of ripening process on quality of k i w i f r u i t has been reported by 0097-6156/89/0405-0305$06.00/0 ο 1989 American Chemical Society

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

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Matsumoto et a l . (3)· Container and s t e r i l i z a t i o n technique i n aseptic packaging of foods i n p l a s t i c or paper-based containers were f u l l y discussed by Toledo (4) and Ito et a l . (5). This paper presents the changes i n chemical constituents of k i w i f r u i t during post-harvest cold storage and ripening under controlled conditions. K i w i f r u i t at optimum canning ripeness were processed by the aseptic canning process with sucrose or high fructose corn syrup as sweeteners. The changes i n starch, sugars, v o l a t i l e s , chlorophylls and organic acids i n the f r u i t during postharvest ripening or after processing are reported.


Experimental Materials and Methods K i w i f r u i t . One hundred kg of k i w i f r u i t (Hayward variety) were harvested at the mature green stage with the soluble solids at 8.0° Brix, and stored at 1°C under 90% r e l a t i v e humidity. The average weight per f r u i t was 81.6 g. The average pressure test (0.794 cm plunger) was 7.5 ± 0.6 kgf. The t o t a l solids content was 16.5%. Ripening. Twelve kg of randomly selected k i w i f r u i t were placed i n glass containers i n a room kept at 20°C. A stream of water-vapor saturated a i r containing 5 ppm ethylene gas was passed over the f r u i t at a rate of 50 ml per minute. The control sample was treated under the same condition except that no ethylene gas was used i n the aeration process. Samples of approximately 2 kg each were taken at designated time intervals for physical and chemical tests. Texture. Firmness of the k i w i f r u i t was measured i n a 10 χ 10 mm peeled area on both cheeks. A U. C. Davis f r u i t pressure tester with a 0.794 cm plunger was used i n the study. The average value of twelve determinations i s reported. Sample preparation. K i w i f r u i t purees were prepared from the hand peeled f r u i t i n a 1°C room after removal of seeds anmd cores. The product was homogenized i n a Waring blender, and frozen immediately in sealed glass jars at -26°C. The frozen purees were thawed and mixed thoroughly before analysis. For the nectars, four repre sentative cans were tested f o r each sample and the average values are reported. pH and t i t r a t a b l e a c i d i t y . An Altex trode was used to determine the pH samples of the k i w i f r u i t puree were water and t i t r a t e d to pH 8.0 with expressed as % c i t r i c acid.

0 70 pH meter with glass elec values of the samples. Ten-g diluted with 100 ml d i s t i l l e d 0.1 Ν NaOH. The results are

Total Solids. The A0AC vacuum oven drying method (6) was used. Five grams of sample were weighed accurately into aluminum dishes using Sartorius #2400 a n a l y t i c a l balance. The aluminum dish con taining diatomaceous earth was dried at 110°C i n an oven, cooled i n desiccator and weighed prior to adding the sample. The loss i n weight after vacuum drying at 70°C f o r s i x hours was determined. The average of three determinations i s reported.


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Chemical Changes in AsepticaUy Processed Kiwi Fruit Nectars

Soluble Solids. A Zeiss Opton refTactometer was used to determine the soluble s o l i d content of the j u i c e at 20°C. The results are reported i n degrees Brix at 20°C. Starch. The Anthrone reagent and iodine colorimetric methods described by McCready et a l . (7) were employed to determine the starch and amylose contents respectively. A Perkin Elmer's Coleman 575 spectrometer was used to measure amylose at 660 nm, and starch at 630 nm.


Ascorbic Acid. The 2,6-dichlorophenol indophenol colorimetric method (11) was used to determine the ascorbic acid content of the samples. Color. A Hunter color difference meter, Model D25D2 was used to evaluate the color of the canned products. A yellowish green porcelain plate, No. C 2 1063 (L - 78.2; a - -2.2; b « +21.7) was used as reference. The Hunter reading was made on the sample i n a c y l i n d r i c a l p l a s t i c port 5.6 cm i n diameter and 3 cm deep. The bottom part of the port was made of colorless p l a s t i c plate of 1.5 mm thickness. A light-trap can coated inside with black coating was used to exclude i n t e r f e r i n g l i g h t from the sample port. The illuminated area was e l l i p i t i c a l (4.1 χ 4.4 cm). Consistency. Consistency of the nectars were measured Brookfield Synchro-Lectric viscometer, Model RVT at 25°C.

with a

Isolation of V o l a t i l e Constituents. The k i w i f r u i t harvested at 8° Brix soluble solids were ripened at 20°C under 90% r e l a t i v e humid i t y i n the presence of 5 ppm ethylene gas f o r 5 days, reaching a soluble solids of 14.5° Brix. The peeled f r u i t were blended at 1°C gently i n a Waring blender. An aliquot of 1.2 kg of blended pulp was diluted with 700 mL d i s t i l l e d water i n a 3-L three neck flask and d i s t i l l e d at 25-30°C under vacuum (1 mm Hg) for 40 hours, y i e l d i n g about 500 mL of d i s t i l l a t e that was collected i n two l i q u i d nitrogen traps. A t o t a l of 3.6 kg of k i w i f r u i t pulp was d i s t i l l e d i n three batches. The d i s t i l l a t e s were combined and frozen immediately u n t i l use. The combined d i s t i l l a t e was extracted i n 250-mL batches f o r 20 hr with 60 mL Freon 11 (bp 23.8°C). The Freon 11 was d i s t i l l e d through a glass d i s t i l l a t i o n column, packed with Fenske helices, prior to use. Each extract was concentrated to approximately to 200 micro L, using a Vigreux column (16 cm), and a maximum temperature of 30°C. Gas Chromatography. A Hewlett-Packard 5880A gas chromatographic unit with a flame ionization detector, equipped with a 60 m χ 0.25 mm i . d . DB-WAX c a p i l l a r y column ( J and W S c i e n t i f i c ; bonded polyethylene glycol phase) was employed. The column temperature was programmed as follows: 30°C hold 2 min to 38°C at l°C/min, then to 180°C at 2°C/min. Hydrogen c a r r i e r gas was used at a flow rate of 1.5 mL/min (30°C). The injector and detector were main tained at 225°C. A modified i n j e c t i o n s p l i t t e r was used at a s p l i t r a t i o of 1:30.


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VEGETABLES


Gas Chromatography-Mass Spectrometry* A VG Trio-2 mass spec trometer was d i r e c t l y coupled with the Hewlett-Packard 589 R gas chromatograph, equipped with a 30 m χ 0.32 mm DB-WAX c a p i l l a r y column (J and W. S c i e n t i f i c ; bonded polyethylene glycol phase). The c a r r i e r gas was He at 2.3 ml/min. The injector and transfer temperature was programmed as follows: 30°C (2 min isothermal), to 38°C at l°C/min, then to 180°C at 2°C/min. The instrument was operated i n the electron-impact mode at an ionization voltage of 70eV. Quantitative analysis by peak area, plots of chromatograms, and l i b r a r y search results were obtained. Sugars. The high performance l i q u i d chromatography (HPLC) method described by Hunt et a l . (8) was used to determine the sugars i n the k i w i f r u i t and nectars with some modifications (21). A Waters Association Chromatograph equipped with a Model 6000-A solvent de l i v e r y system, a Model R401 refTactometer detector, a U6K universal injector column was a 30 cm χ 4 mm i . d . stainless steel tube packed with u-bondapak-carbohydrate (Waters Associates). The precolumn was packed with CO-PELL PAC (Whatman). The eluent was a c e t o n i t r i l and d i s t i l l e d water (85/15, v/v). Five grams of the sample were refluxed with 45 ml of 90% (v/v) ethanol containing a small amount of calcium carbonate for 1 hr at 80°C on a water bath. The mixture was f i l t e r e d through Whitman f i l t e r paper into a round bottom flask, and the residue was recov ered by washing with 80% ethanol. The f i l t r a t e was concentrated to about 5 ml under vacuum at 30°C i n a Rotarvapor-R unit, and diluted to 10 ml i n a volumetric f l a s k . F i n a l l y the solution was f i l t e r e d through a 0.5 micrometer celotate f i l t e r (Millipore Corp.), using a Swinnex s y r i n g e f i l t e r . The i n j e c t i o n volume was 10 m i c r o l i t e r i n a l l cases. Sugars i n the sample were quantified by comparing peak areas of the samples to those of the sugar standards. Chlorophyll. The AOAC spectrophotometric method (9) was used for determination of chlorophyll. A Perkin-Elmer model Coleman 575 spectrophotometer was used to measure the absorbance at 660 and 642.5 nm respectively. The results were reported as chlorophyll, chlorophyll a and chlorophyll b. Organic Acids. The HPLC method for determination of organic acids described by Gancedo and Luh (10) was used. Aseptic Canning. Eight-hundred kg of k i w i f r u i t harvested at 8.0° Brix soluble solids were received from the Alcop Farms, Chico, CA. They were kept at 1°C under 90 r e l a t i v e humidity for two months and then ripened under 90% r e l a t i v e humidity i n the presence of 5 ppm ethylene gas at 20°C for f i v e days. The product was sorted, washed with chlorinated water at 5 ppm free chlorine, and stored at 1°C overnight. A Rietz disintegrator with a 1.25 cm screen was used to break up the f r u i t at 900 rpm. The puree was passed through a Brown juice extractor with a 0.033-inch (0.838 mm) screen to remove skin and seeds. The back pressure i n the Brown j u i c e extractor was set at 4.5 kgf. The juice was pumped through a swept-film heat exchanger with hot water at 91 °C as heating medium, and held for 70 sec i n a 14 meter long, 2.29 cm ID stainless steel tube,


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Chemical Changes in Aseptically Processed Kiwi Fruit Nectars

followed by cooling i n a second swept-film heat exchanger to room temperature (22°C). K i w i f r u i t nectars containing 30, 40, and 50% pulp were prepared using either sucrose or high fructose corn syrup as sweeteners. The f i n a l concentration of the nectars were at 10.5 to 11.5° Brix. The products were a s e p t i c a l l y canned i n the Dole aseptic canning l i n e through heat s t e r i l i z a t i o n at 91°C i n a sweptf i l m heat exchanger, held for 15 seconds, cooled to room tempera ture, and canned a s e p t i c a l l y i n 202 χ 314 (6 oz) cans. The l i d s were s t e r i l i z e d by heating wtih hot a i r at 177°C for 3 minutes before entering the aseptic sealer. Heat s t e r i l i z e d nitrogen gas was used to keep a positive pressure i n the sealer.


Results and Discussion It was necessary to harvest k i w i f r u i t at the mature stage (8.0° B r i x ) , and ripen them under controlled conditions to achieve best sensory quality. When properly handled during harvest and postharvest storage under r e f r i g e r a t i o n at 90% r e l a t i v e humidity, the f r u i t can be kept at 1°C for 5 or more months provided that the storage room i s free from ethylene gas by use of potassium manganate or proper v e n t i l a t i o n with devices to remove ethylene gas ( 12). The standards for grade of k i w i f r u i t have been published by the United States Department of Agriculture i n 1982 (13). The minimum soluble solids content of k i w i f r u i t at harvest time was set at 6.5° Brix. At this stage, the f r u i t s are mature and suitable for cold storage for shipping to distant market under refrigerated storage (14). Seasonal Changes i n Fresh Weight and Ascorbic Acid. The changes i n fresh weight and ascorbic acid of Hayward c u l t i v a r k i t i f r u i t have been studied i n d e t a i l by Okuse et a l . (15). The composition changes i n the developing k i w i f r u i t after f u l l bloom. Starch was the dominant carbohydrate stored i n the c a p i l l a r y tissue and becomes p a r t i a l l y hydrolyzed as the f r u i t reach maturity. Glucose was r i c h i n the green immature f r u i t , but the l e v e l decreased while starch accumulate rapidly during late July and August. As starch hydrolysis began, glucose l e v e l increased rapidly by harvest. Fructose increased gradually from the youngest stage u n t i l harvest. Firmness, Soluble Solids and A c i d i t y Changes. During the postharvest ripening period, the changes i n firmness, soluble s o l i d s , pH and a c i d i t y of k i w i f r u i t at 20°C i n the presence of 5 ppm ethylene gas are shown i n Table I. Table I. Changes i n Firmness, Soluble Solids and A c i d i t y of K i w i f r u i t when Ripening at 20°C with 5 ppm Ethylene

Firmness, kgf ° Brix pH A c i d i t y , as citric, %

0 7.5 7.2 3.28 1.45

1 3.4 9.7 3.32

1.40

Days 2 3 1.8 1.4 12.0 13.2 3.34 3.40 1.38

1.37

4 1.2 13.8 3.42

L.S.D. 5 (p=.05) 0.45 0.1 14.5 0.3 3.42 0.1

1.34

1.28 0.02


3


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Firmness, one of the indicators for ripeness l e v e l was influenced greatly by the presence of 5 ppm ethylene at 20°C. A rapid softening i n texture was observed after ripening for 1 day. Very l i t t l e change was observed i n the control sample which was kept at 1°C without ethylene gas. It has been reported that k i w i f r u i t i s a climacteric f r u i t through the study of i t s physiol o g i c a l changes during growth (16) and post-harvest ripening (17). Ethylene was shown to be produced naturally i n plant tissue from glucose, l i n o l e i c acid and methionine (18). It acts as a plant hormone which controls the ripening process. There are two concepts about f r u i t ripening. F i r s t , ripening occurs due to the increase i n c e l l permeability which leads to the random mixing of enzymes and substrates present i n the tissue. Secondly, the ripening process i s at the f i n a l stage of d i f f e r e n t i a t i o n which i s under genetic control. It involves the programmed synthesis of s p e c i f i c enzymes required for ripening. The influence of ethylene gas on the ripening of k i w i f r u i t was c l e a r l y observed. The sensory quality of k i w i f r u i t was greatly improved, resulting from the softening of the texture, decrease i n a c i d i t y , and increase i n soluble s o l i d content due to the conversion of starch into sugars. In addition to these changes, there were enzymatic reactions which cause formation of more v o l a t i l e s that improve the aroma of the f r u i t . Starch. Starch i s an important polysaccharide present i n f r u i t s such as apple, banana, mango and others. Wright and Heatherbell (19) reported that k i w i f r u i t contains 5-8% starch, and Pratt and Reid ( 17) reported that young k i w i f r u i t has a high starch content. The changes i n starch during ripening at 20°C i n the presence of 5 ppm ethylene are presented i n Table I I . Table I I . Changes i n Starch and Amylopectin During Post-harvest Ripening of K i w i f r u i t at 20°C Component Starch, % (fwb) Amylopectin, % (fwb)

1

2

Days 3

4

5

4.12 2.09

2.40 1.22

1.34 0.60

0.84 0.29

0.65 0.24

Initial 5.56 2.72

It was observed that rapid loss of starch and amylopectin occurred during the f i r s t three days of ripening. The differences were s i g n i f i c a n t at the 95% probability l e v e l . At the beginning, the amylose content was about 50% of the t o t a l starch. It was maintained at that l e v e l during the f i r s t two days of ripening, but decreased to approximately to 40% at l a t e r dates. In the control sample which was kept at 1°C without ethylene gas, only a very small decrease i n starch content was observed. The explanation i s that at lower temperature, the enzyme amylases are less active. Formation of sugars from starch i s one of the important biochemical changes i n the ripening process. Sugars. Fructose, glucose and sucrose are present i n k i w i f r u i t as evidenced by the HPLC method. The changes i n r e l a t i v e amounts during ripening are presented i n Table I I I .


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Table I I I . Changes i n Sugar Content of Ripening K i w i f r u i t During Ripening at 20°C with 5 ppm Ethylene Component

2

1


Fructose, % Glucose, % Sucrose, % Total

Days 3

Initial 3.70 3.68 2.35 9.73

2.80 2.80 1.95 7.55

2.98 2.78 0.52 6.28

4.30 4.28 1.82 10.40

4 4.60 4.71 1.60 10.91

5 4.95 5.04 1.40 11.39

The t o t a l sugar content increases almost i n p a r a l l e l with the increase i n soluble solids during ripening. Fructose and glucose did not increase during the f i r s t day of ripening but gradually increased thereafter. Sucrose content increased rapidly during the f i r s t two days of ripening, but decreased thereafter. In the control sample which was kept at 1°C i n the absence of ethylene, there was no s i g n i f i c a n t increase of sugars during the 5 day storage period. Heatherbell (20) reported that the levels of fructose, glucose and sucrose were 33.2%, 49.3% and 17.5% respectively i n mature fresh k i w i f r u i t . In the present study, fructose and glucose were present at almost i d e n t i c a l level throughout the experiment. However, the sucrose l e v e l i n the ethylene treated samples increased in the f i r s t two days of ripening and then decreased gradually thereafter. I t i s possible that sucrose synthesis occurred i n the ethylene-treated sample i n which starch was acted on by the enzyme phosphorylase. In the l a t e r stage, the enzyme invertase can convert the sucrose into glucose and fructose through enzymic hydrolysis. Chlorophylls. The changes i n chlorophyll content during ripening of k i w i f r u i t at 20°C are presented i n Table IV. Table IV.

Chlorophyll Content of K i w i f r u i t During Ripening at 20°C, mg/100 g Days

Chlorophyll a _b Total a/b

0 3.40 2.95 6.35 1.15

1 3.31 2.90 6.21 1.14

3 3.40 2.99 6.39 1.14

2 3.32 2.93 6.25 1.13

4 3.39 2.93 6.32 1.40

5 2.60 1.70 4.30 1.53

L.S.D. (P-.05) .2 .06

No s i g n i f i c a n t change i n chlorophyll a_ and J> was observed during the f i r s t 4 days of ripening. On the f i f t h day, some changes i n pigments was observed. Thgere was no change i n chlorophylls i n the control sample which was kept at 1°C. The chlorophyll pigments are not stable to heat. The green color disappeared after the canning process largely due to the breakdown of chlorophylls into pheophytins. This was also evidenced by the large change i n a value from -8.1 to +0.3 (see Table VIII). L



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V o l a t i l e Constituents of Ripe K i w i f r u i t . The v o l a t i l e constituents present i n ripe k i w i f r u i t are presented i n Figure 1 and Table V. Through gas chromatography and gas chromatography-mass spectrometry, 39 v o l a t i l e constituents were i d e n t i f i e d i n the f r u i t . These include 13 esters, 13 carbonyls, 9 alcohols and 4 hydrocarbons. The more abundant v o l a t i l e s are: (E)-2-hexenal (peak #28), (E)-2-hexenol (peak #39), ethyl butanoate (peak #13), 1-hexanol (peak #35), hexanal (peak #15), and methyl butanoate (peak #9). They contribute to 93.26% of the t o t a l v o l a t i l e s , largely as unsaturated carbonyls, unsaturated alcohols, saturated alcohol and esters. A l l the other 33 v o l a t i l e s are present i n small amounts. The most abundant v o l a t i l e i s (E)-2-hexenal. Young et a l . (22) reported on v o l a t i l e aroma constituents of k i w i f r u i t grown i n New Zealand. They used vacuum steam d i s t i l l a t i o n and freeze concentration to c o l l e c t the v o l a t i l e s . The concentrated d i s t i l l a t e was analyzed by gas chromatography, gas chromatographymass spectrometry and reaction gas chromatography. According to them, apart from methyl benzoate, a l l the aromatic components i d e n t i f i e d were a l k y l and alkenyl esters, alcohols, aldehydes and ketones. The most abundant component was trans hex-2-enal. Odor evaluation of the components at the exit port of gas chromatograph indicated that ethyl butanoate, hexanal and trans hex-2-enal are important contributors to the aroma of k i w i f r u i t . The flavor of processed k i w i f r u i t , p a r t i c u l a r l y where processing has involved heat treatment, bears l i t t l e resemblance to that of the fresh fruit. Instead, i t i s s i m i l a r to that of the cooked green European gooseberry (Ribes grossularia L ) . Flavor changes also occur during production of k i w i f r u i t j u i c e , even under conditions where heat treatment has been avoided. The method used i n i s o l a t i n g the v o l a t i l e s from k i w i f r u i t i s an important factor causing the difference i n r e s u l t s . Young and Paterson (23) applied quantitative analysis to study the effects of harvest maturity, ripeness and storage on k i w i f r u i t aroma. Their study was very comprehensive and conclusive. They reported 26 aroma compounds i n k i w i f r u i t and concluded that increasing ripeness i s associated with a rapid increase i n the levels of aroma volat i l e s , especially esters, while increasing storage time prior to ripening i s accompanied by a decrease i n the amount of aroma volatiles. They reported the presence of ethanol and limonene i n kiwifruit. These two compounds were not found i n C a l i f o r n i a grown k i w i f r u i t as shown i n Table V. It i s possible that the presence of ethanol may be related to the presence of some moldy k i w i f r u i t which are contaminated with ethanol due to mold growth i n the fruit. The methods of extraction, the solvent used i n i s o l a t i n g the v o l a t i l e s , the equipment i n detecting the v o l a t i l e s , and the ripeness l e v e l of the f r u i t may a l l influence the results on the v o l a t i l e study. By and large, the results from New Zealand are very informative and useful i n the study of sensory quality of kiwifruit. Takeoka et a l . (24) reported i n 1986 that there were 52 volat i l e s present i n k i w i f r u i t , including 11 carbonyls, 9 alcohols, 16 esters, 11 hydrocarbons and one miscellaneous components. They suggested that peak no. 2 was tetrachloromethane which was derived from the solvent used i n the extraction. It i s possible that the presence of toluene (peak #12), p-xylene (peak #20), m-xylene (peak



23. LUH

Chemical Changes in Aseptically Processed Kiwi Fruit313 Nectars

-[ouaxen-e-(z) k

-[puaxàti-e-(a)

3

< M

—?

ο


314


Table V.


Peak no. 3 4 5 6 7 8 9 10 11 13 14 15 16 17 18 19 22 24 25 27 28 29 31 32 33 34 35 36 37 38 39 40 41 42 43 45 46 48 49

V o l a t i l e Constituents of Ripe K i w i f r u i t

Constituent Ethyl acetate Methyl propanoate Methyl 2-methylpropanoate Ethyl propanoate Ethyl 2-methylpropanoate Pentanal Methyl butanoate a-Pinene l-Penten-3-one Ethyl butanoate Ethyl 2-methylbutanoate Hexanal Methyl pentanoate B-Pinene Ethylbenzene (E)-2-Pentenal (E)-3-Hexenal (Z)-3-Hexenal l-Penten-3-ol (Z)-2-Hexenal (E)-2-Hexenal Ethyl hexanoate 1-Pentanol p-Cymene (E)-2-Heptenal (Z)-2-Pentenol 1-Hexanol (E)-3-Hexenol (Z)-3-Hexenol 2,4-Hexadienal (E)-2-Hexenol (Z)-2-Hexenol (E,Z)-2,4-Heptadienal 1-Heptanol (Ε,E)-2,4-Heptadienal Benzaldehyde Methyl furoate Methyl benzoate Ethyl furoate

Kovats Index DB-WAX 890 909 926 961 969 978 987 1015 1020 1040 1056 1081 1087 1095 1119 1124 1139 1144 1170 1196 1210 1236 1261 1263 1317 1329 1363 1370 1389 1393 1413 1423 1461 1465 1486 1512 1575 1613 1621

Peak Area, Rel. Amt., % 0.72 0.03 0.02 0.19 0.04 0.03 2.54 tr 0.07 3.52 0.01 2.78 0.01 0.01 0.03 0.09 0.21 0.04 0.07 0.87 78.00 0.03 0.02 0.01 0.03 0.04 3.40 0.32 0.17 0.01 5.80 0.02 0.03 0.01 0.04 0.02 0.03 0.02 0.01


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#21), o-xylene (peak #26), styrene (peak #30) and naphathelene (peak #51) may have been derived from sources other than the k i w i fruit. Further research on this subject w i l l be of great value as to whether the aromatic hydrocarbons are r e a l l y components of the kiwifruit. Canned Kiwifruit Nectars. The pH, a c i d i t y , Brix and ascorbic acid content of a s e p t i c a l l y processed k i w i f r u i t nectars after storage at 20°C f o r two months are presented i n Table VI.


Table VI. pH, A c i d i t y , °Brix and Ascorbic Acid Content of Canned K i w i f r u i t Nectars Nectar

Kiwi fruit, %

1 50 2 40 3 30 4 50 5 40 6 30 L.S.D. (Ρ-.05)

Sweetener

HFCS HFCS HFCS Sucrose Sucrose Sucrose

PH

Total Acidity, %

°Brix

Ascorbic Acid, mg/100 g

3.45 3.45 3.50 3.45 3.45 3.45 N.S.

0.681 0.545 0.388 0.661 0.519 0.393 0.045

10.5 11.1 10.9 11.5 11.6 11.7 0.9

25.5 21.6 14.4 24.2 20.0 16.1 1.9

The sensory quality of f r u i t nectars depends largely on the pH value, a c i d i t y , and sugar content of the f r u i t at processing time. Control of the ripeness and adjustment of sweetness i n r e l a t i o n to the a c i d i t y are two major procedures i n order to produce high qual i t y nectars. The k i w i f r u i t i t s e l f i s rather strong i n flavor, thus the adding of water and sugars to lower down the a c i d i t y and to improve the sweetness taste w i l l improve the sensory appeal. For most of the f r u i t nectars, the f r u i t content i s now 45% (Standard of i d e n t i t y ) . The former standard was 50% f r u i t i n the nectar. Ascorbic acid retention i n the nectars was improved by the aseptic canning process. Previous work on k i w i f r u i t nectar made by the h o t - f i l l method reported by Wildman and Luh (21) revealed a lower ascorbic acid retention. Thus processing method i s important to retention of ascorbic acid i n the canned product. Consistency. The Brookfield viscosimeter was used to evaluate the consistency of the canned nectars at 25°C. The log-log plots of the Brookfield readings of the nectars i n centipoises vs the speed of spindle No. 2 yields a linear relationship. The speeds used were 5, 10, 20 and 50 rpm. The results are tabulated i n Table VII. The Brookfield values decreased as the spindle speed increased. The phenomenon may be explained by the orientation of the waterinsoluble p a r t i c l e s as the spindle speed increases. The higher speed of the rotation pushes the p a r t i c l e s toward the circumference resulting i n lower Brookfield readings. Results indicate the per cent f r u i t pulp i n the nectar was an important factor influencing the consistency of the product. I f we use the No. 2 spindle rotating at 20 rpm, the corresponding values of the nectars i n cps can be used as an objective measure of the v i s c o s i t y of the product. The sweeteners used here d i d not influence the con sistency as much as the f r u i t pulp percentage.


316


Table VII.

Consistency of canned k i w i f r u i t nectars at 25°C Brookfield Readings i n cps Kiwifruit


Nectar 1 2 3 4 5 6 L.S.D. (P-.05)

5 706.7 392.0 152.0 848.0 365.6 176.0 51.0

50 40 30 50 40 30

rpm 10 404.0 225.2 101.2 508.0 213.2 108.0 45.0

20 330.6 164.6 78.0 312.0 148.0 77.4 32.0

50 209.0 95.6 43.2 206.4 95.4 43.4 19.0

Color. The Hunter color difference meter, Model D25D2 was used to evaluate the color of the canned nectars. The results are shown i n Table VIII.

Table VIII. Nectar 1 2 3 4 5 6 K i w i f r u i t puree L.S.D. (p=.05)

Hunter Color Difference Meter Readings of Canned K i w i f r u i t Nectars Kiwifruit, %

Sweetener

50 40 30 50 40 30 100

HFCS HFCS HFCS Sucrose Sucrose Sucrose None

L 41.1 39.6 37.5 40.7 39.3 37.2 35.9 1.5

a

L +0.3 -0.2 -0.6 +0.1 -0.3 -0.7 -8.1 0.2

b

L +17.3 +16.2 +14.2 +17.3 +15.9 +14.1 +15.6 0.8

Organic Acids i n K i w i f r u i t Nectar. The sensory quality of kiwif r u i t changes greatly with the ripening process i n which the organic acid was metabolized thus increase the pH value of the fruit. According to Okuse et a l . (15), the most abundant organic acid was quinic acid during the e a r l i e r part of the growing season. After ripening the r e l a t i v e amounts of the organic acids d i f f e r greatly from those present i n the mature but under-ripe f r u i t . In the present study i t was found that the major organic acids present i n the ripe k i w i f r u i t s were c i t r i c , quinic and malic acids as analyzed by the HPLC method. The acid contents of the a s e p t i c a l l y canned nectar containing 50% k i w i f r u i t pulp were as follows: c i t r i c acid, 0.295%, quinic acid, 0.247%, and malic acid, 0.150%. These three acids contribute to the a c i d i t y of the k i w i f r u i t .



23. LUH Chemical Changes in Aseptically Processed Kiwi Fruit Nectars Conclusions. The chemical changes i n kiwfruit during post-harvest and ripening can greatly influence the sensory quality of the fresh and canned product. The changes i n firmness, starch, sugars, organic acids and v o l a t i l e compounds during f r u i t ripening are reported i n this paper. Aseptic canning of k i w i f r u i t nectars at 30, 40, and 50% f r u i t levels was accomplished using high fructose corn syrup or sucrose as sweeteners. Proper control of the harvesting, storage and ripening process are the key steps f o r successful processing fo the f r u i t . K i w i f r u i t harvested at 6.5 to 8.0% soluble s o l i d content can be stored under r e f r i g e r a t i o n at 1°C under 90% r e l a t i v e humidity for storage up to 5 or 6 months i f ethylene gas i s removed from the storage room. The stored k i w i f r u i t must be ripened to optimal l e v e l prior to processing. The chlorophyll pigments were changed into pheophytins resulting i n loss i n green color after septic canning. Acknowledgments. The advice of Dr. A. Daniel Jones of the F a c i l i t y for Advanced Instrumentation, University of C a l i f o r n i a , Davis on i d e n t i f i c a t i o n of the k i w i f r u i t v o l a t i l e s by Gas ChromatographyMass Spectrometry i s g r a t e f u l l y acknowledged. The assistance of Mr. Ernest Burton, Irene Fukutome, and Jesus Palma on this work i s greatly appreciated. The author thanks the C a l i f o r n i a K i w i f r u i t Commission of Sacramento, C a l i f o r n i a , for the f i n a n c i a l support of the k i w i f r u i t project. Literature Cited 1. Tillotson, J. E. Food Technology 1984, 38(3), 63-66. 2. Luh, B. S.; York, G. K. In Commercial Vegetable Processing; Luh, G. S. and Woodroof, J. G., Eds.; Avi, Van Nostrand Reinhold: New York, 1988; p 7. 3. Matsumoto, S.; Obara, T.; Luh, B. S. J. Food Sci. 1983, 48(2), 607-611. 4. Toledo, R. T. AIChE Symposium Series, 1982, No. 218, 78, 31-48. 5. Ito, Κ. Α.; Stevenson, Κ. E. Food Technology 1984, 38(3), 60. 6. AOAC. In Official Methods of Analysis, 14th Ed., Assoc. Official Analytical Chemists, Washington, D.C., 1984; p 415. 7. McCready, R. M.; Guggolz, J.; Silviera, V.; Owens, H. S. Anal. Chem. 1950, 22, 1156. 8. Hunt, R. S.; Jackson, P. Α.; Mortlock, R. E.; Kirk, R. S. Analyst 1977, 102, 917. 9. AOAC. In Official Methods of Analysis, 14th Ed., Assoc. Official Analytical Chemists, Washington, D.C., 1984; p 59. 10. Ganado, M. C.; Luh, B. S. J. Food Sci. 1986, 51(3), 571. 11. AOAC. In Official Methods of Analysis, 14th Ed., Assoc. Official Analytical Chemists, Washington D.C., 1984; p 845. 12. Luh, B. S.; Wang, Z. Adv. in Food Research 1984; 29, 279. 13. U. S. Standards for Grades of kiwifruit, U. S. Department of Agriculture, Fed. Register, 1982, 47, p 154. 14. Reid, M. S.; Heatherbell, D. Α.; Pratt, Η. Κ. J. Am. Soc. Hortic. Sci. 1982, 107(2), 316. 15. Okuse, I.; Ryugo, K. J. Am. Soc. Hort. Sci. 1981, 106(2=1), 73-76. 16. Pratt, Η. K.; Goeschl, J. D. Annu. Rev. Plant Physiol. 1969, 20, p 541.


318 17. 18. 19. 20. 21. 22. 23. 24.

QUALITY FACTORS OF FRUITS AND VEGETABLES Pratt, H. D.; Reid, M. S. J . S c i . Fd. Agric. 1974, 25, p 747. Yang, S. F. Hort. S c i . 1980, 15, p 238. Wright, Η. B.; Heatherbell, D. A. New Zealand Agric. Res. 1967, 10, p 405. Heatherbell, D. A. J . S c i . Food Agric. 1975, 26, 815-820. Wildman, T.; Luh, B. S. J . Food S c i . 46(2), 387-390. Young, H.; Paterson, V. J . ; Burns, D. J . W. J . S c i . Food Agric. 1983, 34, 81-85. Young, H.; Paterson, V. H. J . S c i . Food Agric. 1985, 36, 352-358. Takeoka, G. R.; Güntert, M.; Flath, R. Α.; Wurtz, R. E.; Jennings, W. J . Agric. Food Chem. 1986, 34, 576-578. July 14, 1989


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