珍贵鱼类饲料添加剂—抗坏血酸钙生产新工艺的初步研究

本文研究了珍贵鱼类饲料添加剂——抗坏血酸钙的生产工艺。改进了产物结晶的方法。对产品的性状、质量进行了分析,结果表明:抗坏血酸钙生产新工艺简便易行、投资少、设备简单,生产周期短。所得抗坏血酸质量符合FCC(1981)规定标准,产率可达96％以上。     

大肠杆菌中芥蓝抗坏血酸过氧化物酶基因的高效表达

将芥蓝抗坏血酸过氧化物酶(Apx)在大肠杆菌中高效表达。以芸薹属植物apx保守区基因序列为基础,利用PCR,RACE技术从芥蓝中扩增得到全长为753 bp的芥蓝apx编码基因,用DNAMAN V6软件分析该基因氨基酸组成,计算出蛋白分子质量约为27.6 kDa。通过构建重组质粒pET-28a-apx,转化大肠杆菌E.coli BL21,实现了芥蓝Apx的可溶性表达。通过单因素实验优化诱导表达条件,结果表明:0.2 mmol/L IPTG,23℃诱导培养10 h为最佳诱导条件。采用Ni2+亲和层析,纯化了重组蛋白,并得到重组酶最适反应条件为pH 6.5和40℃。为进一步研究Apx的生理特性和功能打下基础。     

α-Tocopherol and Ascorbate Delay Oxymyoglobin and Phospholipid Oxidation In Vitro

An oxymyoglobin liposome model was used to study the effects of α-tocopherol and/or ascorbate upon oxymyoglobin and lipid oxidation. Both oxidations were delayed (P<0.05) by increased concentrations of α-tocopherol alone and α-tocopherol/ascorbate relative to controls. The 14 μ Mα-tocopherol/140 μM ascorbate treatment resulted in greatest delay in both oxymyoglobin and lipid oxidation. Ascorbate alone delayed oxymyoglobin oxidation; effectiveness diminished as ascorbate increased. Ascorbate showed a prooxidant effect toward lipid oxidation which was unchanged in the presence of EDTA. Results support the hypothesis that α-tocopherol retards lipid oxidation directly and OxyMb oxidation indirectly.     

抗坏血酸盐浸渍冷冻对东北冻梨食用品质的影响

目的探究抗坏血酸盐浸渍冷冻处理对冻梨果实食用和营养品质的影响。方法以南果梨为试验材料,分别采用0.5、1.0、3.0 g/L异抗坏血酸钠和0.5、1.0、3.0 g/L抗坏血酸钙溶液进行浸渍冷冻,对制得冻梨果实的色泽、褐变程度、可溶性固形物含量、可滴定酸含量、感官评价、石细胞含量、抗坏血酸含量和总酚含量进行分析。结果与空白组相比,异抗坏血酸钠与抗坏血酸钙溶液浸渍冷冻均可有效改善冻梨果实的色泽,抑制其褐变程度,维持其可溶性固形物含量,提高可滴定酸、抗坏血酸和总酚含量,并降低其石细胞含量,维持其较高的感官品质。结论抗坏血酸钙质量浓度为3.0 g/L时所得冻梨品质最优,为传统东北冻梨加工方式提供了技术支撑。     

The effects of skeletal separation and moisture enhancement for improving the eating quality of cull cow beef

Sixty-two cull beef cows were slaughtered to investigate effects of skeletal separation and moisture enhancement on beef eating quality. Muscles from each carcass side were randomly assigned to 1) no postmortem processing (NPP), 2) prerigor skeletal separation (SS), 3) moisture enhancement (ME) using calcium ascorbate or 4) a combination of SS and ME (SS/ME). Postmortem processing treatment (PPT) by ageing (PM) interactions (P<0.01) for shear force were present for longissimus. As PM ageing increased from 7 to 21 d, there was a greater decrease (P<0.05) in shear force with NPP vs. all other PPT. Trained taste panellists found SS, ME and SS/ME improved (P<0.05) palatability attributes vs. NPP. An additive effect of combining SS and ME improved palatability traits versus SS or ME alone. Panellists found no differences (P>0.14) in softness and tenderness between SS/ME and Canadian AA or AAA beef. Postmortem processing of beef cows may produce beef as tender and juicy as beef from younger carcasses.     

The effect of delay between heat treatment and cold storage on alleviation of chilling injury in banana fruit

BACKGROUND: To understand the mechanisms leading to the enhanced chilling resistance of banana by hot‐water dipping (HWD, 52 °C for 3 min), we investigated the effect of a 0.5–24 h delay between HWD and cold storage on chilling resistance and the change related to the metabolism of reactive oxygen species (ROS). RESULTS: The HWD‐treated fruit with a delay of less than 6 h exhibited markedly less chilling injury than the non‐heated control fruit, while a delay more than 6 h resulted in significant loss in chilling resistance. Increased hydrogen peroxide content and rate of superoxide radical production were detected in the fruit at 0.5–1.5 h after HWD treatment, and the levels declined with a longer delay, which may be correlated with the enhanced gene expression levels of the gene coding for a ROS‐generating related enzyme, NADPH oxidase (MaNOX). Enhanced activities and gene expression of an ascorbate peroxidase (MaAPX) were recorded in the fruit at 1.5–6 h after the treatment, and after 6 h the ascorbate peroxidase levels decayed to the levels as the control fruit. The higher APX gene expression was maintained in the treated fruit with a 3 h delay during the subsequent cold storage at 7 °C, correlating with the enhanced chilling resistance. CONCLUSION: The HWD‐treated fruit left at ambient temperature up to 6 h prior to cold storage maintained the effect of heat treatment and transiently increased ROS content, and the ascorbate peroxidase activity that occurred 0.5–6 h after the treatment may be correlated with the elevated chilling resistance induced by HWD treatment. Copyright © 2012 Society of Chemical Industry     

Quality of Fresh-cut Apple Slices as Affected by Low-dose Ionizing Radiation and Calcium Ascorbate Treatment

ABSTRACT: Although ionizing radiation effectively inactivates food-borne bacterial pathogens in fresh-cut fruits and vegetables, it may adversely affect product quality. In this study, the effects of calcium ascorbate (CaA) and ionizing radiation on quality of 'Gala' apple slices under modified atmosphere packaging were investigated. 'Gala' apple slices, treated with water or 7% CaA followed by either nonirradiation (0 kGy) or irradiation at 0.5 and 1.0 kGy, were stored at 10°C for up to 3 wk. The titratable acidity, pH, firmness, ascorbic acid content, color, and microflora population were measured weekly throughout storage. Irradiation did not affect titratable acidity and pH of sliced apples. Fruit slices softened during irradiation and storage, but this decrease in firmness during storage was reduced by the CaA treatment. Although the ascorbic acid content of apple slices treated with CaA decreased rapidly during storage, the ascorbic acid content was always higher in those treated samples than in the apple slices treated with water. Irradiation decreased both L * and hue values of apple slices. Hue values decreased during the entire storage period while L * increased during the 1st wk of storage, then decreased between 1 to 3 wk of storage. CaA increased L * and hue values of apple slices, suggesting CaA reduced browning, even in irradiated samples. The microflora population of apples slices was not affected by CaA, and CaA treatment did not alter the reduction in microflora by irradiation. The combination of CaA and irradiation enhanced microbial food safety while maintaining quality of fresh-cut apple slices.     

Biochemical aspects of wound healing in yams (Dioscorea spp)

The effects of wounding on the activities of certain enzymes and on the concentrations of selected metabolites were investigated in the tubers of white yam (Dioscorea rotundata). Lipolytic acyl hydrolase activity decreased and disappeared after 4 days whereas the activity of lipoxygenase, peroxidase and polyphenol oxidase increased to a maximum after 1, 4 and 5 days, respectively. The activities of lipoxygenase and polyphenol oxidase were much higher in the proximal half of the tubers than in the distal portion. The increase in lipoxygenase activity at the wound site was a localised phenomenon. The application of the antibiotic, tetracycline, during the early stages of wound healing substantially reduced the increase in the activities of polyphenol oxidase and lipoxygenase. The concentration of free amino acids, total polyphenols and ascorbate increased in response to wounding. Free amino acids steadily declined after 24 h following wounding.     

Physicochemical and Sensory Qualities of Fresh Pork Chops as Affected by Phosphate, Ascorbate or Sorbate Dipping Prior to Irradiation

Fresh pork chops were dipped for a target absorption of 0.5% sodium tripolyphosphate (STPP), 550 ppm sodium ascorbate (SA), or 0.1% potassium sorbate (PS) prior to irradiation (1.0 kGy). Untreated pork chops, both irradiated and unirradiated, were used as controls. Dipping with STPP decreased drip loss and improved color and lipid stability of irradiated chops and resulted in better tenderness and juiciness scores than undipped, irradiated samples. Also, STPP treated chops had similar or better physicochemical and sensory properties than untreated (no irradiation, no dipping) controls. Dipping with SA or PS had little effect compared with STPP, but improved some sensory qualities.     

紫外光谱法研究L-抗坏血酸-2-多聚磷酸酯的稳定性

探讨了影响L-抗坏血酸-2-多聚磷酸酯稳定性的主要因素,利用紫外光谱法研究了酸碱、温度和离子等对其稳定性的影响.