Study On Screening Anti-browning Agents And Mechanism Of Inhibiting The Browning On Fresh-cut Sugarcane And Taro

Enzymatic browning is a big problem,leading to main economic losses in such commodities,especially fresh fruits and vegetables.The deterioration has a significant visual effect as enzymatic browning reduces the commercial quality,the organoleptic acceptance（regarding the appearance of off-flavors）due to the correlated changes in color,flavor,and softening and nutritional value.Currently,novel applied in the food industry include the use of natural compounds with bioactive attributes.These compounds retain the shelf life by preserving the fresh-cut products from browning,texture,and microbial contamination.This research project was divided into four parts:1.In the first part,the objective was to investigate the effects of ethanol on the physicochemical properties and microbial quality of fresh-cut sugarcane.Ethanol（300 mL/L）treatment resulted in the lowest weight loss,electric conductivity,and browning and the best quality attributes in fresh-cut sugarcane.It also significantly reduced the activities of polyphenol oxidase（PPO）,phenylalanine ammonia-lyase（PAL）,and peroxidase（POD）and decreased total phenols and quinines contents.The total bacterial count（TBC）and yeast mold count（YMC）showed that there was significant suppress of microbial spoilage in fresh-cut sugarcane with ethanol treatment.Ethanol treatment increased the CO2 production and decreased O2 level inside the package environment compared to treatments that combined ethanol（300 mL/L）and ascorbic acid（10 g/L）as well as the control（distilled water）.Ethanol was the most efficient approach to inhibiting enzymatic browning and controlling microbial growth on fresh-cut sugarcane.2.In the second part,fresh cut-sugarcane was subjected to ferulic acid solution 2 g/L alone（FA）,FA 2 g/L combined withγ-irradiation 5 kGy（FAIR）,irradiated group 5 kGy（IR）,and not subjected as control（CK）.Quality changes,antioxidant properties,and microbial growth were evaluated for 16 days at 5°C.Ferulic acid treatment significantly inhibited browning of fresh-cut sugarcane discs during storage,accompanied by lower polyphenol oxidase（PPO）,and peroxidase（POD）activity.Furthermore,it induced the activity of phenylalanine ammonia-lyase（PAL）.Whereas,the irradiated treatments（FAIR and IR）significantly stimulated the PAL and POD activity throughout of storage time.In addition,the total phenolic,and flavonoid contents increased significantly,with a concomitant increase highly in DPPH and FRAP values compared to the other.The total bacterial count（TBC）and yeast mold count（YMC）showed that there was significant suppress of microbial spoilage in fresh-cut sugarcane discs with irradiated and ferulic acid treatments compared to control.These results suggested that ferulic acid could be used to maintain the color,quality of fresh-cut sugarcane and extend its postharvest life.3.In the third part,the objective was to investigate the effects of acetic acid（AAD）,and the combination of acetic acid with ethanol（AED）dips on the browning-related enzymes（i.e.,polyphenol oxidase PPO;and phenylalanine ammonia lyase;PAL）,hardness,microstructure change（MC）,microbial count,sensory evaluation,and cell wall modification were also studied throughout subsequences of polysaccharides from alcohol-insoluble residues（AIR）to evaluate cell wall fraction content,molar mass distribution（MM）,and sugar ratios of the taro slices with6-day storage time at 5°C,followed by cooked.The results showed that distilled water dips（DWD）taro slices had significantly（p<0.05）higher activities of polyphenol oxidase（PPO）,phenylalanine ammonia lyase（PAL）,and browning.However,the AAD group had significantly higher hardness compared with the other groups as well as improved sensory scores.Acetic acid dipping pretreated groups showed higher relative percentage of chelate-soluble fraction（CSF）,sugar ratios 2,and 3,and the size distribution of the water-soluble fraction（WSF）and（CSF）than the others pretreated groups.The total bacteria count（TBC）and yeast mold count（YMC）revealed that there was significantly repressed microbial spoilage in taro slices pretreated with AED and AAD groups,respectively.The findings suggested that combination and acetic acid could be used to retain the quality and extend the shelf life;besides,acetic acid alone might be providing an effective method to reduce the softening of thermal processed vegetables.4.In the fourth part,the objective of this study was to improve the solubility of the antioxidant agent,vitamin E（ViE）and vitamin C（ViC）by developing an oil-in-water（O/W）microemulsions（MEs）with food-grade components.The microemulsions were developed and characterized,and its chemical and physical stabilities as well as their antibrowning effects,enzymatic activities of polyphenol oxidase（PPO）and phenylalanine ammonia lyase（PAL）,hardness,total phenolic contents（TPC）,antioxidant properties,and microbial effects in taro slices were investigated during 16 days at 5°C.The microemulsion ViE(ME_ViE)and combination(ME_ViE+0.5%ViC)-loaded microemulsions were demonstrated to be stable after accelerated and long-term conditions.As well as,these treatments significantly（P<0.05）inhibited the increase browning of fresh-cut taro slices,the hardness of taro slices did not change in response to MEs treatments or time in storage,except that taro slices treated with ME_M-4-HB-4-HB at the end of storage decreased,increased the production rate of TPC significantly,and enhanced antioxidant properties during storage（P<0.05）.PPO and PAL activities in the fresh-cut taro slices were also significantly inhibited by ME_ViEiE treated groups（P<0.05）.This study suggested that treatment with ME_ViEiE and combination could inhibit the browning of fresh-cut taro slices by enhancing antioxidant properties to alleviate the oxidative damage.The total bacterial count（TBC）and yeast mold count（YMC）showed that there was a significant decrease of microbial spoilage in both fresh-cut taro with ME_M-4-HB-4-HB and ME_ViE+0.5%ViCiE+0.5%ViC groups.These combined results indicated that MEs of ViE and their incorporation with ViC may be suitable as an anti-browning agent for fresh-cut vegetables.