水杨酸处理对采后番茄果实后熟衰老的影响

研究了不同浓度的水杨酸处理对番茄后熟衰老影响。实验结果表明:与对照相比,0.5mmol/L的水杨酸处理可有效降低果实的乙烯释放量和呼吸强度,并可增加番茄果实的抗坏血酸过氧化物酶(APX)和过氧化物酶(POD)活性,降低相对电导率和腐烂率,保持果实原有颜色和硬度,从而延迟衰老进程;而1mmol/L的水杨酸处理尽管也在一定程度上增加了果实抗病相关酶活性,却刺激了呼吸代谢,加速果实转红和衰老进程。     

超声波协同草酸铵法提取香蕉皮中果胶的研究

该文研究采用超声波辅助草酸铵法提取香蕉皮中果胶的最佳工艺条件,研究了不同草酸铵浓度、料液比、超声功率、超声时间、超声温度和浸提时间对果胶提取率的影响。通过正交试验确定提取香蕉皮果胶的最优工艺条件为:草酸铵浓度0.8%,超声温度65℃,料液比35︰1,超声时间65 min,此条件下香蕉皮果胶的提取率为23.27%。     

微波膨化香蕉脆片的加工

针对市场上真空油炸香蕉片的质量问题 ,本文研究了微波膨化香蕉脆片的可行性。结果表明 :采用威廉斯香蕉 ,通过控制成熟度及护色 ,以 35 %左右含水量香蕉片 ,5 4w/g水分的微波密度进行微波膨化 ,可得到松脆可口、原色原味、无油的香蕉片     

Activities and conformation changes of food enzymes induced by cold plasma: A review

Food endogenous enzymes have impacts on color, texture and flavor of foods during food processing or preservation. Cold plasma is a novel non-thermal food processing technology, which has been extensively studied for contamination elimination and shelf life extension of foods. Particularly, much work has been reported about the effects of cold plasma on enzyme activities and alterations about enzymes conformational structures. It is thus necessary to understand the mechanisms of actions and applications of cold plasma technology in the conformation of food endogenous enzymes. This review focuses on the applications of cold plasma for the inactivation of various endogenous enzymes, including peroxidase, polyphenol oxidase, lysozyme, α-chymotrypsin, alkaline phosphatase, and pectin methylesterase. The activations of several enzymes, such as superoxide dismutase, catalase, and lipase, by cold plasma are also discussed. In addition, this review highlights the transformation of conformational structures including primary and spatial structures induced by chemical reactive species during cold plasma treatments, such as reactive oxygen species and reactive nitrogen species, especially, active sites consisting of prosthetic group and specific amino acids are demonstrated. Both extrinsic and intrinsic factors affecting cold plasma treatments are also described. In general, cold plasma exhibits the ability to activate or inactivate enzymes activities with affecting the conformational structures of enzyme. Further studies should be focused on exploration at molecular level for providing more insight on the interaction mechanism. In addition, equipment and process parameters of cold plasma operation for different fresh food products should be optimized for achieving appropriate control on enzyme variation and obtaining maximum efficiency.     

Giant Amazonian fish pirarucu (Arapaima gigas): Its viscera as a source of thermostable trypsin

A trypsin was purified from pyloric caeca of pirarucu (Arapaima gigas). The effect of metal ions and protease inhibitors on its activity and its physicochemical and kinetic properties, as well its N-terminal sequence, were determined. A single band (28.0 kDa) was observed by SDS–PAGE. Optimum pH and temperature were 9.0 and 65 °C, respectively. The enzyme was stable after incubation for 30 min in a wide pH range (6.0–11.5) and at 55 °C. The kinetic parameters K_m, k_cat and k_cat/K_m were 0.47 ± 0.042 mM, 1.33 s⁻¹ and 2.82 s⁻¹ mM⁻¹, respectively, using BApNA as substrate. This activity was shown to be very sensitive to some metal ions, such as Fe²⁺, Hg²⁺, Zn²⁺, Al³⁺, Pb²⁺, and was highly inhibited by trypsin inhibitors. The trypsin N-terminal sequence IVGGYECPRNSVPYQ was found. The features of this alkaline peptidase suggest that it may have potential for industrial applications (e.g. food and detergent industries).     

Antibacterial effects of natural tenderizing enzymes on different strains of Escherichia coli O157:H7 and Listeria monocytogenes on beef

This study determined the efficacy of actinidin and papain on reducing Listeria monocytogenes and three mixed strains of Escherichia coli O157:H7 populations on beef. The average reduction of E. coli O157:H7 was greater than that of L. monocytogenes and higher concentrations of either protease yielded greater reduction in bacterial populations. For instance, actinidin at 700 mg/ml significantly (p ≤ 0.05) reduced the population of L. monocytogenes by 1.49 log cfu/ml meat rinse after 3 h at 25 & 35 °C, and by 1.45 log cfu/ml rinse after 24 h at 5 °C, while the same actinidin concentration significantly reduced the populations of three mixed strains of E. coli O157:H7 by 1.81 log cfu/ml rinse after 3 h at 25 & 35 °C, and 1.94 log cfu/ml rinse after 24 h at 5 °C. These findings suggest that, in addition to improving the sensory attributes of beef, proteolytic enzymes can enhance meat safety when stored at suitable temperatures.     

Enhanced preservation effects of sugar apple fruits by salicylic acid treatment during post‐harvest storage

BACKGROUND: Salicylic acid (SA) is recognised as an endogenous signal, mediating in plant defense and against pathogens. It has been reported that SA treatment can reduce decay and extend storage life of various fruit, such as bananas, peaches and apples. RESULTS: Physiological and biochemical responses in harvested sugar apple fruit (Annona squamosa L.) to SA at 0.4, 0.8 and 1.2 mmol L^?1 were investigated during post‐harvest storage. Results indicated that SA treatments lowered respiration, increased activities of antioxidant enzymes of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), decreased lipoxygenase (LOX) activity and correspondingly lowered Malondialdehyde (MDA) contents in treated fruits was observed as compared to the control. Moreover, production of superoxide free radical (O₂^{?, ?}) and ethylene was significantly decreased in the treated fruits. Total soluble solids, total soluble sugar, softness and decay rate were significantly lowered in treated fruits, and in turn a delay in the fruits ripening process was achieved after 10 days of storage. CONCLUSION: SA has positive effects in maintaining membrane integrity and in delaying fruit ripening process, which results in improved storability of sugar apple. Copyright © 2008 Society of Chemical Industry     

浓香型大曲水解酶系及测定方法的研究

对浓香型大曲的分解酶体系中的液化型淀粉酶、糖化型淀粉酶、酸性蛋白酶、纤维素酶和木聚糖酶测定方法作了全面的研究。研究发现，（1）大曲不同部位的液化型淀粉酶、糖化型淀粉酶、酸性蛋白酶、纤维素酶、木聚糖酶含量不同，它们主要存在于曲外层。（2）pH值对大曲水解酶活力有影响。发现液化型淀粉酶、糖化型淀粉酶受pH影响较大，而对酸性蛋白酶、纤维素酶、木聚糖酶活力影响较小。（3）测定了不同等级曲的水解酶活力。     

果实成熟软化与相关的酶学研究

果实采后仍然是活的有机体,其后熟软化是一个复杂的生理生化变化过程,其中细胞壁降解酶起着重要的调控作用。综述了与果实成熟软化相关的胞壁酶(多聚半乳糖醛酸酶、纤维素酶、果胶甲酯酶、β-半乳糖苷酶)在果实成熟衰老和软化过程中的作用和活性变化规律,为抑制果实采后软化、延长贮藏期提供理论依据。     

香蕉多糖的抗氧化活性研究

采用40%乙醇溶液和水作为溶剂提取香蕉多糖,并通过比色法检测香蕉多糖对羟基自由基诱导红细胞溶血的影响和对CCl4致小鼠肝脏脂质过氧化抑制效果,研究了其对各种活性氧的抑制或清除作用。实验发现两种方法提取的香蕉多糖均具有明显的抗氧化活性,其中用40%的乙醇提取香蕉多糖对CCl4致小鼠肝组织脂质过氧化和对羟基自由基诱导红细胞溶血的抑制作用较强。