Aili Jiang

Effect of ethanol treatment on physiological and quality attributes of fresh-cut eggplant

BACKGROUND Fresh-cut eggplants, as other vegetables, have relatively short shelf life because of the large amount of tissue disruption and increased metabolism. There is a very rapid onset of enzymatic browning and tissue softening with consequent decrease in sensorial and nutritional quality. To reduce respiration and maintain the quality, various treatments have been applied to find the optimum conditions that provide more fresh and natural fresh-cut produce after minimal processing. The objective of this study was to investigate the effects of ethanol vapour treatment on physiological and quality attributes of fresh-cut eggplant during the extension of shelf life. RESULTS The fresh-cut eggplant treated with ethanol vapour showed that respiration rate and occurrence of enzymatic browning were reduced, and higher total phenol content was maintained during 8 days of storage at 10 degrees C. The polyphenol oxidase and peroxidase in fresh-cut eggplant were also inhibited significantly by ethanol treatment. The ethanol treatment reduced the weight loss and maintained the integrity of cell membranes, as confirmed by the low value of electrolyte leakage. CONCLUSION The ethanol treatment applied for fresh-cut eggplant was a practical approach to reduce the activity of physiological metabolism and maintain the fresh quality of fresh-cut eggplant. The experimental results revealed that ethanol treatment was effective for extending the shelf life of fresh-cut eggplant as a cheap, environmentally acceptable method.

Effect of heat treatment on quality, thermal and pasting properties of sweet potato starch during yearlong storage.

BACKGROUND Proper postharvest handling and storage of sweet potato is an important link in the chain from producer to consumer or manufacturing industry. Heat treatments have been used as a non-chemical means to modify the postharvest quality and reduce pathogen levels and disease development of a wide variety of horticultural products. The objective of this study was to investigate the effects of hot water treatment (HWT) on the quality, gelatinisation enthalpy and pasting properties of sweet potato starch during long-term storage. The weight loss, sprouting, spoilage and sugar content of sweet potato were also determined. RESULTS HWT significantly inhibited the sprouting and decay of sweet potato during the storage period. There were no significant differences (P < 0.05) in the pasting properties and onset (T(O)), peak (T(P)) and endset (T(E)) temperatures of gelatinisation of sweet potato starch among all treatments, especially between heat-treated and non-heat-treated samples. HWT also had no significant impact on the quality of the internal components of the roots. Less than 4% of the yearlong-stored roots were discarded owing to spoilage. HWT supplied a lethal dose of heat to surface pathogens and black spot without damaging the nutritional and processing qualities of sweet potato. CONCLUSION HWT was an effective method to reduce root sprouting and deterioration without significant impact on the quality of the internal components of sweet potato. This novel technique will open a new avenue to extend the storage life of sweet potato with good quality and minimal waste.

Partial Purification and Characterization of A Novel Histidine Decarboxylase from Enterobacter aerogenes DL-1

Histidine decarboxylase (HDC) from Enterobacter aerogenes DL-1 was purified in a three-step procedure involving ammonium sulfate precipitation, Sephadex G-100, and DEAE-Sepharose column chromatography. The partially purified enzyme showed a single protein band of 52.4 kD on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH for HDC activity was 6.5, and the enzyme was stable between pH 4 and 8. Enterobacter aerogenes HDC had optimal activity at 40°C and retained most of its activity between 4 and 50°C. HDC activity was reduced in the presence of numerous tested compounds. Particularly with SDS, it significantly (p < 0.01) inhibited enzyme activity. Conversely, Ca2+ and Mn2+ showed prominent activation effects (p < 0.01) with activity increasing to 117.20% and 123.42%, respectively. The Lineweaver–Burk plot showed that K m and V max values of the enzyme for L-histidine were 0.21 mM and 71.39 µmol/min, respectively. In comparison with most HDCs from other microorganisms and animals, HDC from E. aerogenes DL-1 displayed higher affinity and greater reaction velocity toward L-histidine.