EFFECTS OF PROTEOLYTIC ACTIVITY ON THE CHARACTERISTICS OF AROMATIC RED RICE WINE

The quality of rice wine made from uncooked, unpolished aromatic red rice grain was improved by use of a commercial preparation of acid protease from Aspergillus niger during ethanol fermentation. The fermentation rate of the mash which contained the acid protease was much higher than that of mash that did not contain the preparation of acid protease. The rice wine made from uncooked, polished aromatic red rice, which usually had a less acceptable aroma, was improved by use of the preparation of acid protease, and large amounts of isobutyl alcohol, n-propyl alcohol and ethyl acetate were detected in the resultant rice wine. By contrast, the quality of rice wine made from the bran fraction of aromatic red rice was not improved by the preparation of acid protease. The polished rice fraction of aromatic red rice was affected by the acid protease and the aromatic quality of the rice wine was improved. The aromatic characteristics of red rice wine made from cooked, unpolished aromatic red rice grains, which was rather inferior in terms of both aroma and color, were also improved by the addition of the preparation of acid protease during ethanol fermentation. Thus acid protease has beneficial effects on the production of aromatic red rice wine.     

海藻糖和水分活度对腌制海鳗保藏性能的影响

为考察海藻糖和水分活度对腌鱼保藏的影响,以挥发性盐基氮、三甲胺、细菌总数、酸度和氧化值等为指标采用光度分析方法.结果表明腌制海鳗在水分活度0.8,腌鱼中含海藻糖2%时,腌鱼保藏性能和感官品质最佳.结论:海藻糖具有明显的保鲜作用,控制水分活度是品质关键.     

稻谷储藏中温湿度变化与微生物活动相关性的研究

对不同温度和相对湿度条件储藏的稻谷进行微生物活动和品质监测,实验结果表明,稻谷在30℃、相对湿度70%～80%条件下储藏42d,微生物活动的水平相对较低,没有对储藏稻谷的品质造成明显的影响;当储藏环境相对湿度超过80%后,稻谷中的微生物活动明显增加,储藏21天的微生物活性检测值均可超过500u;特别是当环境相对湿度大于90%时,储藏稻谷的品质将受到显著的影响。高相对湿度环境主要影响储藏稻谷表层的微生物活动,粮层对湿度的扩散有显著的阻挡作用,相对湿度低于90%,30℃、21d 内,不会对0.25m粮层以下稻谷微生物活动产生明显的影响。     

1-甲基环丙烯对黄金梨低温贮藏效果的影响

研究室温条件下,用浓度1.0μL/L 1-MCP处理的黄金梨在低温(0±0.5)℃贮藏过程中呼吸强度、硬度、可溶性固形物、可滴定酸、MDA含量、细胞膜相对透性和PPO活性的变化.试验结果表明:1-MCP处理能明显抑制黄金梨呼吸作用、可溶性固形物、细胞膜相对透性和PPO活性的增加,延缓果实硬度、可滴定酸含量的下降,从而较好地保持果实在贮藏期间的品质和风味.同时降低MDA的含量,延缓果实的成熟和衰老,从而提高黄金梨的贮藏质量.     

WATER ACTIVITY AND TEMPERATURE EFFECTS ON LIPID OXIDATION IN MUSCLE FIBERS

The effects of temperature and water activity on lipid oxidation in washed muscle fibers stored at water activities ranging from 0.96 to 0.70 and at various temperatures were studied. Fluorescence measurements at −20C, revealed no significant change over 50 days at any water activity. At 4C and 20C, there was an initial increase in fluorescence for all samples over the first few days, then a more rapid decrease with no further change up to 40 days. At 80C, no change in fluorescence was seen over a 100-min period. Rancidity did develop in some samples but was not always detected by fluorescence. Through use of oxygen uptake as a measure of lipid oxidation, it was possible to see differences between samples at different water activities and temperatures. However, the limited amount of oxygen and the temperature limitation of the oxygen electrode prohibit studies over extended time periods and at high temperatures (> 50C).     

THE EFFECTS OF STORAGE TIME AND TEMPERATURE ON THE BRUISING OF JONATHAN, DELICIOUS AND GRANNY SMITH APPLES

The resistance to bruising of Jonathan, Delicious and Granny Smith apples decreased with increasing storage time during the 1975 and 1976 seasons. Impact bruise volumes were approximately equal for the three varieties in April. Subsequent testing in June, August and October showed that bruise volumes increased markedly for both Jonathan and Delicious apples and by a small amount for Granny Smith apples. Jonathan apples deteriorated most rapidly and had broken down by October. The resistance to bruising of the three varieties was unaffected by pulp temperature over the range 2°C—30°C. Jonathan, Delicious and Granny Smith apples exhibited strong linear correlations between bruise volume and energy absorbed for all storage times, thus confirming earlier results for Granny Smith apples.     

THE EFFECT OF STORAGE TEMPERATURE ON BACTERIAL GROWTH AND LIPOLYSIS IN RAW MILK

The temperature at which raw milk was stored, within the range 4°-8°C, affected the rate of growth of bacteria and the release of free fatty acids. The effects were of both statistical and practical significance and it was shown that, by maintaining milk temperatures at 4°C, a useful extension of the storage time of raw milk could be achieved. Lipolysis in stored milk was not closely related to the total concentration of psychrotrophic bacteria, but lipolytic rancidity was not observed when the psychrotroph count was below 5 × 10⁶ colony forming units/ml.     

1-MCP处理对新高梨冷藏保鲜效果的影响

以新高梨果实为试材,通过对1-甲基环丙烯(1-MCP)处理新高梨冷藏期间主要生理指标和感官指标变化规律的分析,研究了1-MCP处理对新高梨果实冷藏保鲜效果的影响.结果表明:1-MCP处理推迟了乙烯和呼吸高峰的出现,抑制了果实丙二醛(MDA)和果皮相对膜透性的升高,延缓其衰老,明显延缓了果实硬度的下降,抑制了可溶性固形物含量的升高,从而较好地保持果实在贮藏期间的品质和风味;对照和处理的可滴定酸(TA)含量无明显变化:1-MCP处理可以抑制果心褐变,但经过1-MCP处理却加速了果实的果皮褐变.     

THE INFLUENCE OF STORAGE TEMPERATURE ON THE RESPIRATION OF WATER-IMBIBING BARLEY CORNS

The pattern of respiration of barley in aerated water is influenced by previous conditions of storage. Recently-harvested barley or that stored in the cold gives a respiratory quotient close to 1·0 while barley stored at room temperature for more than 12–18 months gives much higher values. These result from increased levels of alcoholic fermentation and from non-respiratory decarboxylation reactions. The differences between the two types of barley are not related to dormancy or to the vigour of germination. Barley stored in a warm environment shows increased ratios of sucrose to raffinose in the embryo.     

THE USE OF HORDEIN FRACTIONS TO ESTIMATE PROTEOLYTIC ACTIVITY IN BARLEY AND MALT

When the natural barley protein, hordein, is used as a substrate for the assay of exopeptidase and endopeptidase activity in green malts, the enzymic activities found differ significantly from those obtained using non-barley substrates such as dipeptides, gelatin or haemoglobin. Malts having similar total levels of carboxypeptidases as measured using non-barley substrates showed considerable variation in the extent to which these enzymes break down barley hordein. Malts also varied more in their endopeptidase activity with hordein than in their ability to digest gelatin or haemoglobin. Analyses of hordein by gel chromatography and gel electrophoresis indicate that it consists of eight main components, which can be divided into three groups of proteins, with molecular weights in the regions of 15,000, 65,000 and ≥ 100,000. Barley samples differed in their relative contents of these proteins and this variation could be rapidly assessed using gel electrophoresis.     

INACTIVATION OF PAPAIN PROTEOLYTIC ACTIVITY IN THE PRESENCE OF ASCORBIC ACID AND CU++ IONS

The simultaneous presence of ascorbic acid, Cu⁺⁺ ions and oxygen causes reversible inactivation of proteolytic activity of papain. Low concentrations of ascorbic acid and Cu⁺⁺ ions have no effect on their own. Ascorbic acid at concentrations higher than 2 × 10⁻⁴ m inactivates papain irreversibly in the presence of Cu⁺⁺ ions. Papain inactivation is not accompanied by the destruction of papain molecules. Irreversible papain inactivation does not occur in solutions free of oxygen and the intermediates of ascorbic acid oxidation, i.e. dehydroascorbic acid and hydrogen peroxide, do not cause papain inactivation. The irreversible inactivation of papain is most probably due to free radicals formed during ascorbic acid oxidation. Owing to the possible occurrence of both ascorbic acid and Cu⁺⁺ ions in beer, partial irreversible inactivation of papain can be expected even at very low oxygen concentrations.