果蔬多酚氧化酶酶促褐变的控制

在介绍多酚氧化酶酶促褐变原理的基础上,着重阐述通过原料选择、钝化酶活性、抑制酶促反应、改变反应产物、驱氧处理、复合抑制等途径控制果蔬酶促褐变的方法.     

POLYPHENOLOXIDASE ACTIVITY, BROWNING POTENTIAL AND PHENOLIC CONTENT OF PEACHES DURING POSTHARVEST RIPENING

Changes in the polyphenoloxidase (PPO) activity and the phenolic content of peaches (Prunus persica cv. Premier) during postharvest ripening were studied. The fruits were stored at 12 or 25C for up to 15 days. The quantity of extractable proteins was maximum at 6–10 days storage at 25 and 12C, coinciding with the onset of the yellowness in the fruits. The PPO activity increased up to the ripening stage, showing a maximum value at 8 days of storage. This was coincident with the maximum degree of browning as evaluated by the absorbance at 440 nm. The amount of total phenolics and chlorogenic acid in the fruits decreased during storage; however, the differences were not significant. The browning potential closely correlated with the enzyme activity, but not with the phenolic content.     

MICROWAVE BLANCHING OF SLICED POTATOES DIPPED IN SALINE SOLUTIONS TO PREVENT ENZYMATIC BROWNING

Response surface methodology was applied to investigate the way in which variables such as time of treatment, sodium or calcium chloride concentrations and lactic acid concentration affect the microwave blanching of potato slices dipped in these solutions. Two three factor-five-level, second order central composite designs were developed to analyze the considered variables. Results showed that, with reference to polyphenoloxidase inactivation, the blanching in calcium chloride-lactic acid solution was more effective than the blanching in sodium chloride-lactic acid solution. Color measurements showed that, in the applied operative conditions, the best results were obtained by short blanching in sodium chloride-lactic acid solution at high lactic acid concentration and low NaCl concentration and by short blanching in calcium chloride-lactic acid at low lactic acid concentration or low calcium chloride concentration.     

果蔬酶促褐变机理及其抑制方法研究进展

酶促褐变是果蔬深加工过程中存在的一个普遍且很严重的问题.本文介绍了酶促褐变的基本原理、影响因素,并从物理、化学、生物技术等方面介绍了一些酶促褐变的抑制方法.     

COMBINED EFFECTS IN PREVENTING ENZYMATIC BROWNING REACTIONS IN MINIMALLY PROCESSED FRUIT

Fresh sliced apples were dipped in ethanol or cysteine solutions and/or packaged in air or modified atmosphere in order to retard oxidative browning. Modified atmosphere packaging was effective in inhibiting darkening for at least nine days at refrigerated storage conditions. The combination ethanol dip/modified atmosphere packaging resulted as a suitable method in maintaining the original color in apple slices even after exposure to air.     

ENZYMATIC BROWNING IN MARULA FRUIT 1: EFFECT OF ENDOGENOUS ANTIOXIDANTS ON MARULA FRUIT POLYPHENOL OXIDASE

Spectrophotometric assays of marula fruit polyphenol oxidase showed a pronounced lag phase due to the presence of endogenous antioxidants. The total antioxidant capacity (TAC) was quantified in terms of the equivalent concentration of L‐ascorbic acid (L‐ASC.eq). Freeze‐dried marula fruit juice had 2960 mg L‐ASC.eq. per 100 g (pH 4.5) or 1872 mg L‐ASC.eq per 100 g of sample (pH 7.0) assayed with ABTS. The values compare with the known L‐ASC content of 2017 mg per 100 g. The vitamin C content of marula fruit accounts for about 70% of the TAC. The TAC estimate for marula fruit was 20–40 times greater than levels reported in most other fruits.     

THE EFFECT OF PRETREATMENT OF SHREDDED CELERIAC USING SOLUTIONS OF ENZYMATIC BROWNING INHIBITORS ON THE QUALITY OF MINIMALLY PROCESSED PRODUCT

ABSTRACT

The study investigated the effect of soaking celeriac flakes in solutions containing various concentrations of enzymatic browning inhibitors on the quality of stored minimally processed product. Ascorbic acid (0.2–0.5%), 4‐hexylresorcinol (0.003–0.01%), sodium chloride (0.1–0.5%) and sodium lactate (2–3%) were used as browning inhibitors. On the basis of the conducted tests, it was found that among the applied browning inhibitors, only ascorbic acid had an advantageous effect on the quality of stored celeriac flakes. Along with an increase in its concentration in the solution (0.2–0.5%) used for the pretreatment of the flakes, the value of color parameter a* decreased, while the value of parameter b* increased. At the concentration of ascorbic acid in the solution exceeding 0.25%, flake color in the sensory examination was evaluated as desirable. An increase of ascorbic acid concentration in the solution in the range from 0.2 to 0.4% resulted in a decrease in the total mesophilic and psychrophilic bacteria counts, respectively, by 3 and 1 log cfu/g of the stored product.

PRACTICAL APPLICATIONS

Minimal processing of celeriac provides convenience for consumers and many economic benefits for producers. Minimal processing of celeriac can induce disadvantageous changes in tissue, which may lead to darkening of the flakes and deterioration of product sensory attributes. Moreover, shredded raw material constitutes an excellent medium for the development of microorganisms. This article contains information about the effectiveness of enzymatic browning inhibitors for extending the shelf life of celeriac flakes. We show a range of concentrations of inhibitors, which improve the preservation of color, intrinsic taste and microbial quality of minimally processed celeriac.