KINETICS OF HYDROXYMETHYLFURFURAL ACCUMULATION AND COLOR CHANGE IN HONEY DURING STORAGE IN RELATION TO MOISTURE CONTENT

Quality reduction in honey during storage is indicated by hydroxymethylfurfural (HMF) accumulation and darkening of color. The effects of moisture content and temperature on HMF accumulation and color change in honey during storage were investigated. HMF accumulation and color change followed first- and zero-order reaction kinetics, respectively. The moisture content affected the rate of the two degradation reactions depending on the storage temperature. Reduction in moisture content caused an increase in rate constant for HMF accumulation at 20 and 30C, but there was no significant effect of moisture content at 40C. Rate constants for change in lightness and total color change values increased with increasing moisture content at 20 and 30C. The highest rate constant for change in color values was obtained at a moisture content of 18% at 40C.

PRACTICAL APPLICATIONS

Hydroxymethylfurfural accumulation and color change are two major quality degradations in honey during storage. This study shows that the rates of these two degradations are dependent on moisture content of honey. In addition, effect of moisture content on the rates of reactions was dependent on temperature of storage. Therefore, producers need to consider the effects of both moisture content and storage temperature in reducing quality loss in honey during storage.     

NUTRITIONAL ESTIMATION OF CHANGES IN MINERAL CONTENT DURING FROZEN STORAGE OF WHITE ASPARAGUS

Nine essential elements (copper, iron, zinc, manganese, calcium, magnesium, sodium potassium and phosphorous) were determined in white asparagus (Asparagus officinalis, L.) by flame atomic absorption spectrophotometry in order to examine the possible variations in mineral content caused by frozen storage at ?18C for 45 and 90 days. Statistically significant differences were determined during frozen storage for all the mineral elements investigated, except for Ca, Mg, Na and P which did not exhibit any significant differences (p>0.05) and, together with Zn, showed no significant modifications under frozen storage. A diminution in Cu, Fe, Mn and K concentrations was observed during the frozen storage time. Statistically significant differences were established between thicknesses of the asparagus spear in the content of Cu, Fe, Zn, Ca, Na and K and it was seen that the thickness of the asparagus did not fit any specific model. Between portions, all the elements studied displayed statistically significant differences in their concentrations, except for Ca and K (p>0.05) and, for all the minerals elements analyzed, the highest levels were found in the apical portion of the asparagus spear, except for Na with a higher content in the basal portion. White asparagus is an adequate food source of mineral elements, except for Na, and frozen storage does not cause any great variations in the percentages of mineral RDAs (Recommended Dietary Allowances) supplied.     

CHANGES OF POLYAMINE CONTENT IN CHINESE CABBAGE DURING STORAGE IN AIR OR LOW OXYGEN ATMOSPHERE

Endogenous levels of polyamines, including putrescine, spermidine, and spermine, were determined in the outer laminae, outer midribs, inner laminae, and inner midribs of Chinese cabbage (Brassica campestris L. Pekinensis group) during storage at 0°C in air or in 1% O₂ atmosphere. In the outer laminae where tissues were more mature, polyamines declined linearly with storage at 0°C. The content declined more slowly in low oxygen-stored samples than in air-stored samples. In the inner laminae where tissues were still meristematic, polyamines in both air- and low oxygen-stored samples showed a quadratic response and increased during the first 6 weeks of storage. Thereafter, the level of polyamines decreased under both treatments, but a higher level was maintained in the low oxygen-stored samples.     

莲雾采后贮藏期间生理变化的研究

采后莲雾在贮藏期间失水严重，硬度迅速下降；呼吸速率先降后升；果肉细胞膜透性在采后初期急剧上升；果实的可溶性固形物、蛋白质和Vc的含量一直呈下降趋势，室温贮藏4d后莲雾的商业品质迅速下降。     

CHANGES IN THE RESPONSE TO GIBBERELLIC ACID OF BARLEY ENDOSPERM SLICES DURING STORAGE

Endosperm slices representative of freshly harvested as compared with stored barleys produce relatively little α-amylase when treated with gibberellic acid (GA). The response is improved by suitable storage, by heating or by procedures which increase oxygen supply to the aleurone cells. No difference could be detected in the response to GA of the dehusked corns of the two types of barley. It appeared that the outer coverings of the freshly harvested barley restrict the permeability to oxygen to a greater extent than those of stored barley, possibly because of higher microbial activity.     

ALTERATION IN LIPID OXIDATION OF CHANNEL CATFISH DURING FROZEN STORAGE IN RESPONSE TO ASCORBATE APPLICATIONS

Channel catfish were treated with ascorbate via metabolic absorption and vacuum tumbling. The fillets were subjected to varying periods (0, 1.5, 3, 4.5, and 6 months) of frozen storage at −6C. When muscle ascorbic acid levels were increased two fold by both methods, TBA-RS values were significantly lower than that of the control after 6 months of storage. Vacuum tumbled fillets with muscle ascorbic acid that increased by four fold were found to be the least stable to oxidation. The possible fate of the ascorbic acid in the fish tissue was discussed.     

EFFECT OF PHYSIOLOGICAL MATURITY AT HARVEST ON PEACH QUALITY DURING LOW TEMPERATURE STORAGE

Peaches (cvs ‘Loring’ and ‘Redglobe’) were collected from five packinghouses within a 20 km radius on a single harvest date. Using color chips to categorize harvest maturity, fruit color and firmness were evaluated on the day of harvest. After 7 day storage at 5°C, designed to simulate maintenance of a cold-chain during wholesale distribution, peach color, firmness and sensory quality were determined. Color and flavor development were inhibited at 5° C but the softening rate increased at increasing levels of maturity. Separation of softening from flavor and color development has implications in study of ripening physiology of the peach and in assessing current handling practices.     

CHANGES IN QUALITY ATTRIBUTES OF LONGAN JUICE DURING STORAGE IN RELATION TO EFFECTS OF THERMAL PROCESSING

Longan juice is accepted gradually by consumers due to its unique succulent, sweet and aromatic flavor. The effects of thermal processing (91C, 20 min) on quality related attributes (color, translucency, total soluble solids, total acidity, reducing sugars, ascorbic acid, phenolic compounds, protein and pectin) of longan juice during storage at low temperature were investigated. The heat-treated longan juice had a higher translucency and lower concentrations of pectin, phenolic compounds and proteins of longan juice, compared with the nonheat-treated juice. Furthermore, the thermal processing maintained higher concentrations of total soluble solids and total acidity but a lower ascorbic acid concentration. However, the thermal processing had no significant effects on reducing sugar concentration. Overall, the thermal processing maintained effectively color appearance and nutritional attributes such as total soluble solids and total acidity of longan juice during storage at low temperature. These results suggest that the thermal processing exhibits a potential for quality maintenance of longan juice.

PRACTICAL APPLICATIONS

Browning and turbidity are the major factor to influence quality of fruit juice during storage. Thermal processing is generally applied to improve quality and extend shelf life of fruit-related products. In this study, application of thermal processing exhibited potential for quality maintenance of longan juice in terms of evaluations of color, translucency and concentrations of total soluble solids, total acidity, reducing sugars, ascorbic acid, phenolic compounds, protein and pectin. The information obtained from this study could be used as a guideline for designing thermal processing to control the quality of longan juice.     

EFFECT OF OIL CONTENT ON THE LOSS OF ALPHA-ACID FROM HOPS DURING STORAGE

Examination of a wide range of hop varieties showed that the percentage loss of α-acid in storage was related to the essential oil content of the samples. Seedless hops, having higher oil contents, lost more α-acid than seeded hops of the same variety. The variety Bullion grown for isomerized extract manufacture should be picked 7–10 days earlier than normal to minimize loss of α-acid before processing.     

CONTRIBUTION OF PHOSPHOLIPIDS TO HEADSPACE VOLATILES DURING STORAGE OF PECANS

The relationship between headspace volatiles and lipid class fatty acid composition was investigated in pecans subjected to room temperature storage for 8 months. During early stages of storage, pentanal predominated in the pecan headspace, whereas at later stages hexanal predominated. Quantities of triacylglycerols recovered from pecans did not change significantly during storage, whereas a decrease in phospholipid content and an increase in free fatty acid content were seen. While losses of polyunsaturated fatty acids (PUFA) in triacylglycerols and free fatty acids only occurred during the last month of storage, PUFA losses were recorded in the phospholipid fraction by 5 months. Based on a strong negative correlation (R =?0.98) between hexanal and its precursor fatty acid (18:2) in phospholipids, the results suggested that membrane lipids would be a primary site of attack during the early stages of oxidation. Future studies with oilseeds, such as pecans, should therefore examine the possibility that variations in phospholipid fatty acid composition could explain cultivar differences in storage stability.     

COLOR CHANGES IN WAXED TURNIPS DURING STORAGE1

Turnip (Brassica campestris, L. var. rapifera) roots were stored unwaxed and waxed with a water-miscible, carnauba-based wax in vented plastic bags or in cardboard produce boxes for 6 weeks. Packaging turnips in plastic bags reduced weight loss during storage more effectively than waxing or storing in boxes. The purple color of the turnips faded regardless of package used; waxing temporarily darkened and intensified the purple color. The white or cream portion of the roots was not affected by waxing but became light tan when roots were stored in boxes. The chroma of the white portion increased during storage regardless of package or wax treatment. These results indicate that the external purple color of the turnip root was unstable during storage and this color loss was independent of weight loss.     

COLOR CHANGES IN BANANAS AND PLANTAINS DURING STORAGE

Two cultivars, namely Cavendish bananas (Musa AAA Group) and plantains (Musa AAB Group) were used to study the changes in their peel color during storage at various temperatures. Gas-treated and nontreated fruits, and the L* a* b* system were used. The temperature effect on the color parameters was mainly through the interaction with the gas treatment, variety and storage time; however, redness (a*) for gas-treated bananas was expressed as a *=−20.1 + 0.14TD, (T= temperature, D = day). Similarly, a*=−27.5 + 55 (TD)^1/2− 0.2 T D, predicted the degreening process in gassed plantains. The gas-treatment, storage time and variety all had a significant effect (p<0.01) on the L*a*b* parameters. Plantains lost the greenness during storage faster than bananas.