低温结合气调包装对荔枝保鲜作用

本文探究了常温条件下不同浓度的嘧菌酯和甲基硫菌灵对采后荔枝果实保鲜效果的影响,在贮藏期间通过对荔枝生理指标进行分析从而筛选出较优的杀菌剂配方,并对筛选后的杀菌剂配方进行验证以及膳食暴露评估,最终获得可以在常温贮藏条件下延长荔枝货架期的保鲜方法。结果发现,在25 ℃贮藏条件下,采用25%嘧菌酯1600倍稀释液（M1600）、25%嘧菌酯1600倍稀释液复配70%甲基硫菌灵700倍稀释液（M1600+J700）处理荔枝可以显著抑制果实的呼吸强度（P<0.05）,降低果皮的相对电导率（P<0.05）和果实的腐烂率（P<0.05）,且在一定程度上抑制了果肉中可溶性固形物TSS和维生素C含量的降低,较好地维持了荔枝果实的感官品质和食用价值。经对比发现,两种杀菌剂对荔枝的保鲜效果相当,但单独使用M1600在抑制荔枝果皮褐变方面效果较优。通过对贮藏期间荔枝全果和果肉中杀菌剂残留量的检测以及膳食暴露评估发现,单独使用嘧菌酯处理荔枝后整果中嘧菌酯的风险熵RQ远小于1,可以同时达到满足提高荔枝贮藏品质、安全食用以及降低经济成本的目的。该研究为荔枝等非呼吸跃变型果实采后品质提升的研究提供了技术参考。

     

充氮处理对荔枝酒氧化褐变的影响研究

为减少荔枝酒贮藏过程中的氧化褐变,本实验对荔枝酒采用充氮封瓶处理,通过测定相关指标,并结合HPLC分析,发现经充氮处理的荔枝酒褐变指数A420和酚类物质相对聚合度分别较对照（未充氮）下降了46.3%和26.8%,而总酚损失减少,其中（-）-表儿茶素、原花青素B2、绿原酸及芦丁的损失分别比对照（未充氮）减少了49.5%、31.1%、22.6%和23.2%,说明充氮处理通过减少荔枝酒中的溶解氧,减少了酚类物质的氧化聚合程度,从而在一定程度上延缓了荔枝酒的褐变。      

影响荔枝汁非酶褐变的因素及其控制方法

通过测定荔枝汁加工和贮存过程中褐变度的变化,研究了影响荔枝汁非酶褐变的主要因素。结果表明,影响荔枝汁非酶褐变的主要因素有:多酚类物质、pH值、金属离子(Mg2+、Fe3+、Cu2+、Sn2+)、包装材料和贮藏温度。通过控制这些因素可有效抑制荔枝汁的非酶褐变。     

大孔吸附树脂抑制荔枝酒褐变的研究

研究了大孔吸附树脂应用到荔枝酒中的防褐变效果。通过考察LSA-900C、LSA-800B和XDA-5三种树脂的静态吸附时间、料液比、吸附温度对荔枝汁总酚含量、色度及香气的影响,确定LSA-900C为较合适的吸附处理树脂,吸附条件为料液比3∶200¹∶20,温度20³0℃,时间5¹0min;采用LSA-900C分别吸附荔枝汁及荔枝酒,考察其防褐变效果及感官品质,结果表明,发酵后吸附比发酵前吸附所得荔枝酒在贮存过程中更加不易褐变,且感官品质更佳,因此采用LSA-900C大孔树脂在发酵完成后处理荔枝酒能有效减缓褐变且较少影响荔枝酒的品质。      

包装材料对贮藏期荔枝汁品质及非酶褐变的影响

研究了聚酯(PET)瓶、聚乳酸(PLA)瓶和聚酯/铝箔/聚乙烯(PET/Al/PE)复合袋装荔枝汁在25℃避光贮藏时的品质变化和非酶褐变情况,采用偏最小二乘法回归(PLSR)分析包装材料对荔枝汁非酶褐变的影响。结果表明:贮藏过程,PLA瓶装荔枝汁的L-抗坏血酸(L-AA)发生快速降解,PET瓶和复合袋中的L-AA降解缓慢;贮藏初期,溶解氧浓度(DOC)均急剧下降,贮藏后期,除PLA瓶中的DOC快速上升外,其它包装材料中的DOC均平缓下降并趋于稳定。包装材料阻隔性能对L-AA含量和DOC有显著(p<0.05)影响。蔗糖不断水解,果糖和葡萄糖含量在贮藏初期快速地增加,然后缓慢下降。氨基酸总量和总酚含量不断下降。可溶性固形物(TSS)含量缓慢上升,pH缓慢下降。5-HMF含量和褐变指数不断上升。包装材料阻隔性能使得荔枝汁中的溶解氧浓度差异,溶解氧能引起L-AA的降解和酚类物质氧化聚合,导致荔枝汁发生非酶褐变。     

Purification of polyphenol oxidase and the browning control of litchi fruit by glutathione and citric acid

Polyphenol oxidase (PPO, EC 1.10.3.2) was purified to homogeneity from litchi peel yielding a single protein with a molecular weight of about 75.6 kD by Sephadex G‐100 gel filtration, and a 108‐fold purification of PPO achieved. The enzyme was determined to be composed of two similar subunits. Glutathione, L ‐cysteine and citric acid suppressed PPO activity markedly, whereas ascorbic acid and n‐propyl gallate showed a little inhibition. Moreover, the effect was enhanced by the addition of citric acid. On the basis of the inhibition of PPO activity in vitro, the use of 10 mmol l ⁻¹ glutathione and 100 mmol⁻¹ l citric acid was found to give good control of the browning of litchi fruit, and an 80–85% inhibition of PPO activity was observed. It is suggested that application of glutathione in combination with citric acid may slow down the browning of litchi fruit. © 1999 Society of Chemical Industry     

Effect of pure oxygen atmosphere on antioxidant enzyme and antioxidant activity of harvested litchi fruit during storage

The effects of pure oxygen on pericarp browning, reactive oxygen species (ROS) metabolism, antioxidant enzyme and antioxidant activity of harvested litchi fruit were investigated. Application of pure oxygen significantly prevented pericarp browning and delayed the increase in membrane permeability of litchi fruit during storage. Litchi fruit exposed to pure oxygen showed a lower level of lipid peroxides, compared to control fruit, with the delay in the increases of both H₂O₂ content and superoxide production rate. Furthermore, it was found that the treatment with pure oxygen induced the activities of superoxide dismutase (SOD), ascorbated peroxidase (APX) and catalase (CAT), which could be beneficial in scavenging of H₂O₂ and superoxide and alleviating lipid peroxidation. In addition, antioxidant ability (reducing power and free-radical scavenging activity against DPPH radical, superoxide anions and hydroxyl radical) of methanol extracts from litchi fruit pericarp declined gradually, with decreasing contents of anthocyanins and phenolic compounds, as storage time of the fruit progressed. There was a linear relationship between the contents of either anthocyanins or phenolic compounds and antioxidant ability or free radical scavenging activity. Treatment with pure oxygen markedly increased antioxidant ability, which was related to higher levels of anthocyanins and phenolic compounds, compared with those of control fruit. It is suggested that enhanced antioxidant activity and antioxidant enzyme induced by pure oxygen may contribute to alleviating lipid peroxidation and maintenance of membrane integrity, which reduced decompartmentation of enzymes and substrates, resulting in enzymatic browning.     

Effects of heat treatment on internal browning and membrane fatty acid in loquat fruit in response to chilling stress

BACKGROUND: Chilling injury (CI) limits the storage period and shelf‐life of red‐fleshed loquat fruit (Eriobotrya japonica Lindl.), which leads to a remarkable loss after cold storage. To develop an effective technique to reduce CI, the effects of a 38 °C heat treatment in air for 5 h, plus storage at 1 °C for 35 days, on internal browning (IB) and membrane fatty acid composition of the loquat cv. Jiefangzhong were investigated. RESULTS: Heat treatment delayed the occurrence of IB and inhibited the increase of IB index in ‘Jiefangzhong’ loquat fruit. Heat treatment maintained lower levels of electrolyte leakage and malondialdehyde content, and inhibited the increases in phospholipase D and lipoxygenase activities compared with the control fruit. Meanwhile, heat treatment inhibited the increases in palmitic, stearic and oleic acid levels and delayed the decreases in linoleic and linolenic acid contents, thus maintaining higher unsaturated/saturated fatty acid ratio than the control. CONCLUSION: These results suggest that the reduction of IB in chilled loquat fruit by heat treatment might due to maintenance of membrane integrity and higher unsaturated/saturated fatty acid ratio. Copyright © 2010 Society of Chemical Industry     

Screening quality and browning susceptibility of five artichoke cultivars for fresh‐cut processing

BACKGROUND: Artichoke is a rich source of bioactive compounds, mainly phenols, in the Mediterranean diet, but its consumption is limited by the complexity of time‐consuming trimming operations. Fresh‐cut processing would therefore add convenience to its consumption, even though the severity of post‐cutting browning of artichoke pieces is still a major problem. Since susceptibility to browning may vary widely among genotypes, the choice of the cultivar is a very critical step in the fresh‐cut process. In this study, five different Italian cultivars (C3, Catanese, Tema, Violetto Foggiano and Violetto Sardo) were screened for their initial quality and composition, and their post‐cutting performance during storage at 5 °C and 20 °C. RESULTS: C3 showed the highest phenol content (3.4 g GA kg^?1) and antioxidant activity (24.5 mmol L^?1 kg^?1), but the worst quality in terms of appearance and colour changes, also due to its high PPO activity (62.2 U g^?1). Catanese showed the highest vitamin C content (117.7 mg kg^?1), the lowest phenol content (1.8 g GA kg^?1), and the best post‐cutting quality. Tema, Violetto Foggiano and Violetto Sardo showed an intermediate phenol content, the latter showing the lowest appearance score after C3. CONCLUSION: These results confirmed the role of phenols in browning processes of fresh‐cut artichokes, giving the first available information on artichoke cultivar suitability to be processed as a fresh‐cut product. Copyright © 2009 Society of Chemical Industry     

Effect of ozone and calcium lactate treatments on browning and texture properties of fresh‐cut lettuce

The effects of three treatments, 1 mg L^?1 ozone at 18–20 °C, 15 g L^?1 calcium lactate (CLac) at 50 °C and a combination thereof, were compared on fresh‐cut lettuce over 10 days of refrigerated storage. Respiration rate, browning and texture were examined as main quality indicators. The use of ozone produced a significantly (P < 0.05) higher oxygen decline than the use of CLac (from day 3 to day 10). At the end of storage, CLac (alone or combined with ozone) samples had higher oxygen content (～9%) than ozone samples (～6%). Enzymatic activity decreased significantly (P < 0.05) in ozone samples. Polyphenol oxidase activity in fresh‐cut lettuce treated with ozone (alone or combined with CLac) showed lower values on day 1 (<2500 units g^?1) and at the end of storage (<3000 units g^?1) than CLac samples (4000–4800 units g^?1). Ozone also reduced peroxidase activity to ～300 units g^?1 after treatment. Finally, pectin methylesterase activity was also reduced with ozone, showing a negative effect on textural properties. Data suggested that CLac maintained quality markers better than treatments with ozone and ozone/CLac combination over 10 days of storage. Copyright © 2006 Society of Chemical Industry     

Comparative study of browning and flavan‐3‐ols during the storage of white sherry wines treated with different fining agents

White sherry wines were treated with three fining agents (activated charcoal, PVPP and Riduxhigh), in addition to an initial treatment with casein and bentonite, in four different combinations. The wines were stored at 20 or 30 °C for 1 year with a view to examining changes in their flavan‐3‐ol fraction and differences in their degree of sensitivity to browning. Flavan‐3‐ol monomers and dimers, as well as browning measured as absorbance at 420 nm, increased during storage in all the wines. After this period the wines treated with fining agents containing activated charcoal, PVPP and Riduxhigh exhibited less marked browning, with no significant differences among them at both 20 and 30 °C. However, taking into account the higher initial colour of bottled wines treated with Riduxhigh in relation to those treated with activated charcoal or PVPP, this fining agent showed higher capacity to control browning. © 2000 Society of Chemical Industry     

A combination of hot air treatment and nano‐packing reduces fruit decay and maintains quality in postharvest Chinese bayberries

BACKGOUND: Chinese bayberry is susceptible to microbial decay during postharvest handling and storage. To search for effective alternatives to currently used fungicides for disease control, the efficacy of hot air (HA) treatment at 48 °C for 3 h alone or in combination with nano‐packing (NP) containing nano‐TiO₂ and nano‐Ag in controlling green mould decay caused by Penicillium citrinum and natural decay, and their effects on fruit quality in harvested Chinese bayberries were investigated in this study. RESULTS: The combined treatment of HA and NP resulted in a remarkably improved control of green mould and natural decay in Chinese bayberries compared with treatment of HA or NP alone. The in vitro growth of P. citrinum was significantly inhibited by individual HA or NP. In addition, HA in combination with NP showed interactive effect on inhibiting fruit respiration, ethylene production and membrane lipid peroxidation, and maintained higher fruit firmness and DPPH radical scavenging activity. CONCLUSION: These results suggest that a combination of HA treatment and NP may be a useful technique to reduce fruit decay and maintain quality in Chinese bayberries during postharvest storage and retail conditions. Copyright © 2010 Society of Chemical Industry