中式绿茶硬质干酪工艺的研究

研究了绿茶粉风昧干酪的制作工艺,结果表明,绿茶风昧干酪的最佳工艺条件为绿茶粉加入量1%,原料乳采用75℃,15s杀菌,冷却后加入2%的发酵剂,其中保菌和嗜菌比例为1:2,发酵温度为35℃。当发酵乳pH值至5.8时停止发酵,在发酵乳中加入0.02%的CaCl_2和1.5g/L的混合凝乳酶(动物凝乳酶和微生物凝乳酶比例为4:1),35℃条件下凝乳1h后经排乳清,加盐后熟化得到干酪产品,产品膻味大大降低,出品率为9.78%。     

Effect of Organic Acids and Plant Extracts on Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium in Broth Culture Model and Chicken Meat Systems

ABSTRACT:  Foodborne illness due to consumption of products contaminated with  Salmonella  Typhimurium ( S .T.),  Listeria monocytogenes  ( L.m. ), and  Escherichia coli  O157:H7 ( E.c. ) results in many deaths and significant economic losses each year. In this study, acetic (AA), citric acid (CA), lactic acid (LA), malic acid (MA), and tartaric acid (TA) and grape seed (GS), green tea (GT), bitter melon seed (BMS), rasum, and fenugreek (FG) extracts were investigated as inhibitors against  S .T.,  L.m.,  and  E.c . in both broth-culture and meat systems. Brain Heart Infusion solutions containing 18.7, 37.5, and 75.0 mM organic acids and 5, 10, 20, and 40 mg/mL extracts were challenged with approximately log 6 CFU/mL  S .T.,  L.m ., and  E.c . A pH-adjusted control was included to determine pH effect on exhibited antibacterial activity. For the meat system, 1 to 2 g chicken breast pieces were vacuum-infused with CA/MA/TA acid at 75 and 150 mM and GS and GT at 3000, 6000, and 9000 ppm in a partial factorial arrangement. GT and GS showed considerable activity in broth-culture. All organic acids were effective in broth-culture at 75 mM after 24 h ( P  < 0.05). CA and TA were effective at 37.5 mM. CA/MA/TA at 150.0 mM were the most effective in the meat system, reducing  E.c. ,  L.m.  and  S. T. by >5, >2, and 4-6 log CFU/g, respectively, although all organic acids showed some antibacterial activity at 75.0 and 150.0 mM. These findings demonstrate the effectiveness of organic acids and plant extracts in the control of  S .T.,  L.m ., and  E.c.  O157:H7.     

Effect of irradiation on the antioxidative and antigenotoxic activities of a green tea leaf and stem extract

Green tea (Camellia sinensis) leaf and stem extract, a major byproduct of the green tea industry, was investigated for its antioxidative and antigenotoxic activities after 20 kGy of irradiation. In vitro antioxidative activities, including 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging, hydrogen peroxide inhibition, tyrosinase inhibition activities, and the reducing power were tested. Green tea leaf extract (GTLE) had higher antioxidative activities than the green tea stem extract (GTSE). Irradiation of 20 kGy to GTLE showed a decreasing tendency in DPPH radical, hydrogen peroxide‐scavenging activities, and reducing power, while that to GTSE showed an increasing tendency of the antioxidative activities. Tyrosinase inhibition activity showed no difference on irradiation, in GTLE and GTSE. Overall, irradiation had positive influences on the antioxidative activity in the GTSE more than in the GTLE. Antigenotoxic effect of the green tea extracts on an oxidative DNA damage in human leucocytes by a DNA comet assay also indicated a protective effect of GTLE. The irradiated GTLE began to decrease the DNA damage significantly at 10 μg mL^?1, which showed a higher inhibition activity than the non‐irradiated GTLE. The non‐irradiated and irradiated GTSE showed similar inhibition trends and they were comparable with that of the GTLE. Results suggest that the extract of GTSE, a major byproduct of the green tea industry, can be considered as a cost‐effective functional ingredient for industrial applications. Furthermore, irradiation of the GTSE may have beneficial effects on its functional activity.     

Antioxidant activity of various extracts of old tea leaves and black tea wastes (Camellia sinensis L.)

The antioxidant activity of various extracts of old tea leaves (OTL) and black tea wastes (BTW) in comparison with that of green tea leaves (GTL) was evaluated. The highest extraction yield and antioxidant activity were found in hot water extracts of GTL. Hot water extracts of OTL and BTW showed the same statistically significant antioxidant activities (P < 0.05). Also, there was no statistically significant difference between the antioxidant activities of OTL and BTW extracts obtained by the other two extraction methods (ethyl acetate and methanolic methods) and, in some cases, BTW extracts acted even better than OTL extracts. The antioxidant activity of tea extracts was not concomitant with the development of their reducing power. This suggested that the antioxidant activity of tea extracts likely involves other mechanisms in addition to those of reductones. Totally, BTW extracts had antioxidant activities comparable with or even better than those of OTL extracts. Hence, OTL and BTW, which are often considered as agricultural wastes, can be used as potent natural antioxidative sources.     

乙醇——离子联合沉淀法分离茶多酚及果胶类物质的新工艺

介绍了一种乙醇———离子关合沉淀法制备茶多酚的新工艺，并对工艺过程进行优化。在最佳工艺条件下，茶多酚的收率可达到１２．１％，纯度达９２．３％。同时初步探讨了乙醇———离子联合沉淀法除果胶类物质的机理。     

Studies on radical scavenging activity of tea leaves and effect of additives on activities of black tea liquor

Green tea is proved to be a source of various biochemicals, which projects tea to be a health drink. The study investigated free radical scavenging activity of leaf extracts of south Indian tea clones, individual catechin molecules and documented the influence of various additives on the scavenging activity of black tea infusion. Among the tea clones, UPASI-17 contained higher quantum of catechins. Lower content of catechins correlated with low 1,1-diphenyl-2-picrylhydrazyl and hydroxyl scavenging activities. Low scavenging activity was noticed in gallocatechin. A wide variation was found in free radical scavenging activity of individual molecules, leaf extracts, tea liquor and its combination with the additives. Tea liquor along with lemon juice showed the highest free radical scavenging activity. When sugar and lemon juice were amended with tea liquor, free radical scavenging activity declined marginally. Addition of milk and sugar with tea liquor declined the free radical scavenging activity significantly.     

茶多酚水提与醇提的比较研究

通过实验研究比较了茶多酚水提与醇提两种工艺的优缺点。采用正交试验,比较相同因素水平下水提与醇提茶多酚的提取率,结合生产成本,对两种工艺进行优劣评价。结果：同等条件下,醇提的效果好于水提,如果茶多酚需进一步通过树脂柱纯化,则水提工艺的后续成本低于醇提。结论：生产含量较低的茶多酚,宜选用醇提;生产高纯度的茶多酚,宜选用水提。     

Effects of cosolvents on the decaffeination of green tea by supercritical carbon dioxide

Due to the adverse effects of the caffeine in a variety of plant products, many methods have been explored for decaffeination, in efforts to remove or reduce the caffeine contained in plant materials. In this study, in order to remove caffeine from green tea (Camellia sinensis) leaves, we have employed supercritical carbon dioxide (SC–CO₂), which is known to be an ideal solvent, coupled with a cosolvent, such as ethanol or water. By varying the extraction conditions, changes not only in the amount of caffeine, but also in the quantities of the principal bioactive components of green tea, including catechins, such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC), were determined. The extraction conditions, including temperature, pressure and the cosolvent used, were determined to affect the efficacy of caffeine and catechin extraction. In particular, the type and concentration of a cosolvent used constituted critical factors for the caffeine removal, combined with minimal loss of catechins, especially EGCG. When the dry green tea leaves were extracted with SC–CO₂ modified with 95% (v/v) ethanol at 7.0 g per 100 g of CO₂ at 300 bar and 70 °C for 120 min, the caffeine content in the decaffeinated green tea leaves was reduced to 2.6% of the initial content. However, after the SC–CO₂ extraction, a substantial loss of EGCG, as much as 37.8% of original content, proved unavoidable.     

凝固型羊奶茶加工技术的研究

以羊奶粉和茶粉为主要原料，对影响凝固型羊奶茶加工的因素进行了研究。通过单因素试验、正交试验确定凝固型羊奶茶的最优配方：羊奶粉60％，植脂末25％，白砂糖15％，羔羊皱胃酶0．12％，绿茶粉2％，乳酸钙0．15％，卡拉胶0．1％（均为质量分数，下同）。该产品食用方便，用50℃的温水稀释4倍，静置4-7min后即可凝固食用。