Effects of high-pressure treatment on the extraction yield, phenolic content and antioxidant activity of litchi (Litchi chinensis Sonn.) fruit pericarp

As a promising technique, high-pressure extraction (HPE) method was used to extract bioactive compounds from litchi fruit pricarp. The study involved in different experimental factors such as solvent, ethanol concentration (35-95, v/v), material to solvent ratio (1:25-1:100, w/v), acidic medium, extraction pressure (200-500 MPa), time (2.5-30 min) and temperature (30-90 °C). The extraction yield, total phenolic contents, 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and superoxide anion scavenging capability of the HPE sample were examined and then compared with those of ultrasonic extraction and conventional extraction samples. The application of HPE obtained higher extraction yield compared to other extraction methods. However, there were no significant differences ( P  >   0.05) in the total phenolic content and the antioxidant activities among these various extractions. Compared with some conventional extraction method, the HPE exhibited higher extraction efficiency in terms of higher extraction yield and extraction time.     

Effect of oxalic acid on control of postharvest browning of litchi fruit

Litchi (Litchi chinensis Sonn.) fruit, cv. Huaizhi, was treated with 2 and 4 mM oxalic acid and stored at room temperature to investigate the effect of oxalic acid on pericarp browning. The results showed that the pericarp browning indices of the fruit, treated with both oxalic acid concentrations, were significantly lower than that of the control, due to increase of membrane integrity, inhibition of anthocyanin degradation, decline of oxidation, and maintanance of relatively low peroxidase activity in the fruit during storage. It appears that application of oxalic acid can effectively control the pericarp browning of litchi fruit during postharvest storage.     

ATP-regulation of antioxidant properties and phenolics in litchi fruit during browning and pathogen infection process

The impact of energy level on antioxidant properties in relation to pericarp browning and loss of disease resistance of litchi fruit was investigated. Litchi fruits were vacuum-infiltrated with distiled water (control), 1 mM adenosine triphosphate (ATP) and 0.5 mM 2,4-dinitrophenol (DNP) under 75 kPa for 3 min before being inoculated with Peronophythora litchi or not. ATP-treated fruits presented higher activities of antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX). Higher activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging, reducing power and contents of phenolic compounds were also observed in ATP-treated fruit during storage. In contrast, DNP treatment lowered the enzymes activities, scavenging ability and the contents of phenolic compounds. Higher levels of antioxidant enzymatic system and non-enzymatic system were observed in P. litchii-inoculated fruits than those in non-inoculated fruits. Application of ATP and DNP exhibited a similar change patterns and effects in inoculated fruits. When related to previously reported ATP levels, the results suggested that ATP levels could regulate the antioxidant system. Sufficient available energy is crucial for inhibiting browning and preventing the loss of disease resistance in harvested litchi fruit.     

Fruit quality and physiological responses of litchi cultivar McLean's Red to 1-methylcyclopropene pre-treatment and controlled atmosphere storage conditions

The effect of 1-MCP pre-treatment and two different controlled atmosphere storage conditions (CA-1, 17% O₂ + 6% CO₂; CA-2, 7% O₂ + 3% CO₂) on fruit quality parameters and physiological changes with respect to pericarp browning in ‘McLean's Red’ litchi were investigated. Fruits were pre-treated with 1-MCP (500 nl/l) and held at CA-1 or CA-2 for 21 d at 2 °C and at 90% RH. Stand-alone CA-1 or stand-alone CA-2 and the commercially adopted sulphur dioxide (SO₂) treatment were included in this study for comparison. Of the five treatments 1-MCP + CA-1 was most effective in preventing browning, loss of red colour (colour value a*) of the pericarp, ascorbic acid content; and retaining acceptable SSC/TA and taste. Fruit from 1-MCP + CA-1 showed higher overall acceptance after 21 d storage without any off-flavour according to the sensory panel data.1-MCP + CA-1 reduced the polyphenol oxidase (PPO) and peroxidase (POD) activity, retained membrane integrity and anthocyanin content during storage. Although SO₂ treatment prevents browning it showed negative effects on SSC/TA, taste and membrane integrity. Stand-alone CA-2 condition indicated higher pericarp browning, PPO, POD activity and loss of membrane integrity. Therefore, 1-MCP pre-treatment and CA-1 retains overall fruit quality for up to 21 d.     

成熟度对晚香蕉李冷藏条件下果实品质的影响

采收不同成熟度的晚香蕉李冷藏,研究了成熟度对晚香蕉李贮藏品质的影响。结果表明:成熟果实能维持较高总糖、VC和可溶性固形物(TSS)含量,但果实膜透性、丙二醛含量和硬度较低。未成熟Ⅱ果实总糖、VC和TSS含量与成熟果实接近,果实硬度较高,贮藏后期仍能维持较低膜透性,为贮藏最佳成熟度。     

Effect of thermal and high hydrostatic pressure processing on antioxidant activity and colour of fruit smoothies

Fruit smoothie samples were thermally treated (P₇₀ ≥ 10 min) or high hydrostatic pressure (HHP) processed (450 MPa) with holding time of 1, 3 or 5 min and antioxidant activity, phenolic content and colour values (L*, a* and colour intensity) were determined. Significant reductions in antioxidant activity (p < 0.001) and phenolic content (p < 0.001) were observed at the applied pressure and a maximum treatment time of 5 min. Mean values for redness (a*) showed an increase (p < 0.001) in HHP processed smoothies compared to fresh. As expected, storage also had a significant effect on colour variables but the effect was more pronounced in high pressure treated samples stored for 30 days. Both colour and antioxidant activity were significantly affected by high pressure processing. Therefore, process optimisation of high pressure systems should be considered by processors prior to its adoption as a preservation technique in order to minimise the effect on the quality of fruit smoothie products.Industrial relevanceFruit smoothies have become popular with consumers and may significantly contribute to daily antioxidant intakes. Thermal processing has been shown to reduce the antioxidant activity of fruits, thus non-thermal methods of pasteurisation such as high hydrostatic pressure processing could help retain antioxidants in fruit smoothies offering a unique selling point for processors. The present study focussed on assessing the effect of thermal and high pressure processing on the antioxidant activity and phenolic content of fruit smoothies. Since decreases in levels of antioxidants were noted during long term storage it would appear that higher pressure treatments (> 450 MPa) might be required for better retention of antioxidant compounds in fruit smoothies.     

Influence of processing and storage on the antioxidant activity of apple derivatives

The antioxidant activity of seven apple varieties was determined on fresh fruits and processed products (dried fruits and purees) and during storage. The antioxidant activity of apples correlated with the total phenol concentration but not with ascorbic acid concentration. Apple derivatives showed a lower antioxidant activity than the counterparts of the fresh fruits and the occurrence of browning phenomena during processing resulted in lower antioxidant activity. Dried fruits showed higher antioxidant activity per gram of dried matter than fruit purees probably because of the lower total thermal effect of processing. The antioxidant activity of all products increased within the first month of storage, and then declined. The extent of early increase was related to the polyphenol content of the fruit. Packaging conditions further influenced the antioxidant activity increase during storage possibly by affecting the oxygen availability.     

Changes in phenolic composition and antioxidant activity of white wine during bottle storage: Accelerated browning test versus bottle storage

Polyphenol content, antioxidant activity, reducing power, colour and changes during storage over nine months in bottles and after accelerated browning were studied in selected Hellenic varietal white wines. The following phenolic compounds were identified in the wines: Caftaric, coutaric, fertaric, ferulic, caffeic, p-coumaric and gallic acids, (+)-catechin and (−)-epicatechin. The results showed that the contents of most of the phenols diminished with time, with the exception of caffeic, ferulic and p-coumaric acids. Antioxidant activity increased with storage whereas reducing power remained significantly unaffected. Accelerated browning did not significantly alter the concentrations of tartaric acid esters but it increased the concentrations of the hydroxycinnamic and gallic acids. (+)-Catechin concentration was not affected while (−)-epicatechin decreased. Antioxidant activity did not show any significant change but reducing power was reduced after the end of the browning test. As for the absorbance at 420 nm, it remained unchanged during storage, but it was significantly increased after accelerated browning.     

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。

     

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     

Effects of high hydrostatic pressure processing and subsequent storage on phenolic contents and antioxidant activity in fruit and vegetable products

Fresh fruits and vegetables have been reported to possess a variety of bioactivities partly due to their high abundance of phenolics. However, traditional thermal pasteurisation during fruit and vegetable processing typically induces a pronounced loss of phenolic compounds. In contrast, nonthermal pasteurisation techniques, especially high hydrostatic pressure (HHP) processing, are beneficial to the retention of phenolics. In addition to more effectively keeping original freshness, flavour and colour of fruit and vegetable products to the greatest extent, in most cases, HHP processing and subsequent storage more effectively sustain the levels of phenolic compounds and antioxidant activity in fruit and vegetable products compared with thermal pasteurisation. Therefore, HHP processing has a huge potential to preserve fruit and vegetable products rich in phenolic compounds.     

南酸枣糕贮藏过程中非酶褐变的研究

为了解决南酸枣糕贮藏过程中的非酶褐变问题,以南酸枣糕为研究对象,对其在7周贮藏期间内,不同温度下褐变指数及影响褐变的主要物质的含量变化进行研究。结果表明,褐变指数和5-羟甲基糠醛的含量变化与温度和贮藏时间呈正相关,还原性抗坏血酸、总酚的含量变化与温度和贮藏时间呈负相关。低温贮藏条件下,还原型抗坏血酸氧化反应是南酸枣糕贮藏过程中主要的褐变反应,当温度升高至30℃,美拉德反应是酸枣糕贮藏过程中导致褐变的主要因素。      

Effect of storage temperatures on antioxidant capacity and aroma compounds in strawberry fruit

The antioxidant capacity (measured as oxygen radical absorbance capacity, ORAC), total anthocyanins, total phenolics, aroma compounds, and postharvest quality of strawberry fruit (Fragaria x ananassa cv. Chandler) kept at 0°C, 5°C, and 10°C were investigated. Strawberry fruit stored at 10°C or 5°C showed higher antioxidant capacity, total phenolics, and anthocyanins than those stored at 0°C. However, the postharvest life based on overall quality was longer at 0°C than at 5°C or 10°C. The production of aroma compounds was markedly influenced by storage time and temperature. Individual aroma compounds were affected differently. For example, ethyl hexanoate, hexyl acetate, methyl acetate, and butyl acetate increased, while 3-hexenyl acetate and methyl hexanoate decreased during storage. In general, strawberries stored at 10°C or 5°C produced higher levels of these volatiles than those stored at 0°C. In conclusion, strawberries stored at 0°C retained an acceptable overall quality for the longest storage duration; however, berries stored at temperatures higher than 0°C showed higher content of aroma compounds and antioxidant capacity during the postharvest period.     

Antioxidant activities and contents of polyphenol oxidase substrates from pericarp tissues of litchi fruit

The experiments were performed to extract and purify substrates for polyphenol oxidase (PPO) from pericarp tissue of postharvest litchi fruit. Two purified PPO substrates were identified as (−)-epicatechin and procyanidin A2. The antioxidant properties of two PPO substrates were further evaluated in the present study. Variation in the content of the major substrate (−)-epicatechin of litchi fruit during storage at 25 °C was analysed using the HPLC-UV method. The results showed that (−)-epicatechin exhibited stronger antioxidant capability than procyanidin A2, in terms of reducing power and scavenging activities of DPPH radical, hydroxyl radical and superoxide radical. Furthermore, (−)-epicatechin content in pericarp tissue tended to decrease with increasing skin browning index of litchi fruit during storage at 25 °C. Thus, these two compounds can be used as potential antioxidants in litchi waste and the fresh pericarp tissue of litchi fruit exhibited a better utilisation value.     

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。     

自发气调对鸭梨果实生理生化品质的影响

以鸭梨为试材,研究了自发气调贮藏(MAP)对果实采后生理品质的影响。结果表明,MAP贮藏增加了鸭梨果实贮藏期间的黑心病发生率,贮藏结束时,MAP贮藏果实的黑心指数较对照提高了78%。MAP贮藏增加了果实多酚氧化酶的活性,减少了总酚的含量。MAP贮藏还抑制了果实内过氧化氢酶和抗坏血酸过氧化物酶的活性,MAP贮藏果实较对照果实具有较高的丙二醛和过氧化氢含量。      

Effect of integrated application of chitosan coating and modified atmosphere packaging on overall quality retention in litchi cultivars

BACKGROUND: The storage life of litchi is limited due to pericarp browning and decay. Modified atmosphere packaging (MAP) showed promising results for ensuring quality retention. However, to improve the efficiency of MAP the integrated treatment of a chitosan coating and MAP was investigated. RESULTS: The effect of chitosan (1.0 g L⁻¹) + MAP was compared with MAP (control), and was effective in preventing decay, browning and retaining the pericarp colour in the cultivar McLean's Red. Chitosan (1.0 g L⁻¹) + MAP significantly reduced polyphenol oxidase (PPO) and peroxidase (POD) activity, retained membrane integrity, anthocyanin content and prevented the decline of pericarp colour values during storage. The POD activity was greater than the PPO activity in the cultivars McLean's Red and Mauritius. The two cultivars differed in anthocyanin content and the activity of oxidation enzymes. The gas compositions within the packages were compared between chitosan at 1.0 g L⁻¹ and 20.0 g L⁻¹ concentration for both cultivars. Chitosan (20.0 g L⁻¹) + MAP lowered the respiration during storage in both cultivars compared to 1.0 g L⁻¹ + MAP. CONCLUSION: The McLean's Red cultivar is better suited for chitosan (1.0 g L⁻¹) + MAP integrated treatment than is Mauritius in retaining overall quality. Copyright © 2009 Society of Chemical Industry