A proposed mechanism for the inhibition of soybean lipoxygenase by β‐carotene

The inhibition mechanism of soybean lipoxygenase (LOX) by β‐carotene was studied. Addition of β‐carotene into the reaction mixture decreased the rate of conjugated diene formation. Increasing the concentration of β‐carotene in the reaction mixture resulted in a decrease in the rate of conjugated diene formation. Although the rate of conjugated diene formation was lower in the presence of β‐carotene, the same amounts of linoleic acid hydroperoxides were formed by the enzyme at the end of the reaction, both with and without β‐carotene in the reaction medium. The rates of conjugated diene formation for 40, 20, 10 and 4 U mL^?1 LOX enzyme were almost equal to zero when the concentrations of β‐carotene were 20, 17.5, 15 and 10 µmol L^?1 in model reaction systems, respectively. β‐Carotene directly influences the amount of enzyme in the reaction medium available for the catalytic conversion of linoleic acid into corresponding hydroperoxides. The results obtained here suggest that β‐carotene reacts with linoleyl radical (L^?) at the beginning of the chain reaction, preventing the accumulation of conjugated diene forms (LOO^?, LOO^? and LOOH). Since L^? transforms back to its original form of LH, the enzyme cannot complete the chain reaction and thus remains at inactive Fe(II) form. Copyright © 2005 Society of Chemical Industry     

Co-oxydation of linoleic acid to volatile compounds by lipoxygenase isoenzymes from soya beans (author's transl)]

Lipoxygenase isoenzymes L-1 (optimum pH 9.0) and L-2 (pH 6.5) were incubated with linoleic acid. The extracted volatile compounds were separated by gas-chromatography and analysed by mass spectrometry. The relative amounts of volatile carbonyl compounds, which were formed during catalysis were determined (mole percent). L-1 yielded hexanal (greater than 90% at pH 7 and 70% at pH 8.5). L-2 at pH 7 yielded hexanal (31), two geometric isomers of 2,4-decadienal (40), 2-trans-heptenal (12) and 2-trans-octenal (10).     

Effect of the absence of lipoxygenase isoenzymes on the storage characteristics of rice grains

Three varieties of paddy rice with and three varieties without lipoxygenase (LOX) isoenzymes were stored at room temperature, in dark conditions for 42 months. Insect damage and viability were investigated during that time. Varieties without LOX-1,2 and their offspring were screened with a rapid method of estimating LOX isoenzymes, and subjected to an accelerated-ageing experiment. The results indicated that in varieties without LOX-1,2, after long storage, rice quality was normal, but for varieties with LOX-1,2, rice quality deteriorated. With increase of storage time, the germination rate of the seed of most varieties decreased greatly except for varieties without LOX-1,2 where there was almost no change in the germination rate. In varieties without LOX-1,2 and their offspring, after an accelerated ageing experiment the germination rate of some varieties changed slowly, but with others, the germination rate changed quickly. This indicated that a definitive factor, which influenced the life of seeds, may be the loss of LOX-1,2. During storage, there was also a significant difference in the degree of insect damage. In varieties without LOX-3 insect damage was lower, but in varieties with LOX-3 insect damage was higher. Therefore, the absence of LOX-3 may be very important in insect resistance in rice grain.     

氧化铝吸附提纯大豆卵磷脂的工艺研究

以溶剂粗提后的大豆卵磷脂粗品为原料,采用氧化铝吸附法进行提纯。系统考察了氧化铝用量、乙醇用量、吸附时间和吸附温度等因素对大豆卵磷脂粗品中磷脂酰胆碱(PC)纯度及回收率的影响,得到最佳工艺条件为:大豆卵磷脂粗品与氧化铝质量比为1∶5,大豆卵磷脂粗品与无水乙醇配比为1∶60(m/v),吸附时间60min,吸附温度30℃。在此条件下,PC的纯度和回收率分别为70.23%和83.07%。      

氧化铝吸附提纯大豆卵磷脂的工艺研究

以溶剂粗提后的大豆卵磷脂粗品为原料,采用氧化铝吸附法进行提纯.系统考察了氧化铝用量、乙醇用量、吸附时间和吸附温度等因素对大豆卵磷脂粗品中磷脂酰胆碱(PC)纯度及回收率的影响,得到最佳工艺条件为:大豆卵磷脂粗品与氧化铝质量比为1∶5,大豆卵磷脂粗品与无水乙醇配比为1∶60(m/v),吸附时间60min,吸附温度30℃.在此条件下,PC的纯度和回收率分别为70.23％和83.07％.     

胡萝卜素的柱层析法测定

试样中胡萝卜素经丙酮－石油醚提取，以氧化镁为吸附剂，丙酮－石油醚脱剂分离，比色测定。由于标准胡萝卜素的不稳定性，经实验采用标准Ｋ２Ｃｒ２Ｏ７替代，使测定方法简便，稳定。     

HPLC法测定复方保健酒中人参皂苷和西红花苷的含量

采用高效液相色谱仪建立测定复方保健酒中人参皂苷Rg₁、人参皂苷Rb₁、人参皂苷Rb₂、人参皂苷Rc、西红花苷I、西红花苷II含量的方法。结果表明,最佳测定条件为采用Agilent SB-Aq色谱柱(4.6 mm×250 mm,5μm),以乙腈-水为流动相梯度洗脱,流速1.0 mL/min,柱温30℃,人参皂苷的检测波长203 nm,西红花苷的检测波长为440 nm,进样量10μL。人参皂苷Rg₁、人参皂苷Rb₁、人参皂苷Rb₂、人参皂苷Rc、西红花苷I、西红花苷II在各自浓度范围内线性关系良好(R≥0.999 9),平均加标回收率97.83%～101.72%,精密度试验结果相对标准偏差(RSD)0.43%～1.85%。实验结果表明该方法操作简单,精密度和准确度高,重复性好,可用于复方保健酒中人参皂苷和西红花苷含量测定。     

Co-oxidation of beta-carotene and canthaxanthine by purified lipoxygenases from soya beans (author's transl)]

Isolation and purification of soya bean lipoxygenase (linoleate: O2 oxidoreductase, EC, 1.13.11.12) on Sephadex G-200, DEAE-cellulose and by isolectric focusing yields two isoenzymes of the L- 2 type (optimum pH 6.5) and two of the L-1 type (optimum pH9.0). Different crude extracts from soya beans as well as the purified L-2 isoenzymes exhibit the same capacity for co-oxidation of beta-carotene and canthaxanthine, when the comparison is based upon equal lipoxygenase activities. In contrast to L-2 the alkaline lipoxygenase L-1 is a poor "carotene oxidase".     

Composition and characterization of soyabean and related products

Soyabean contains about 48 to 50% proteins. Among these, storage proteins are predominant. 7S and 11S globulins are two storage proteins that constitute 80% of the total protein content in soyabean. Moreover, there are other less abundant storage proteins such as 2S, 9S, and 15S globulins. In addition to globulins, enzymes, protease inhibitors (Kunitz and Bowman‐Birk), lectin, and others complete the soya protein content.

Different methods exist to characterize soya proteins. These methods involve (1) an isolation of proteins from soya commercial products and (2) the use of analytical techniques for protein determination.

Soya proteins may interact with other soya components such as minerals, phytic acid, ascorbic acid, and fiber. These interactions, which depend on soya processing and treatment, can decrease the bioavailability of minerals and proteins.

Swelling, solubility, viscosity, and capacity to form a gel, an emulsion, or a foam are the main functional properties of soyabean. They are responsible for the wide use of soya in industrial processes.     

低强度超声间歇浸取栀子黄色素

研究了时间、温度、功率、频率等因素在单频、双频复合和双频交变超声浸取时对栀子黄色素质量浓度的影响.并用包括温度、时间、功率、乙醇浓度、粒度、固液比和超声频率(28、40、50、135kHz)等影响因子的混合水平均匀设计实验优化双频组合超声浸取工艺,用标准化回归系数评价了温度、功率、频率等关键因素对目标参数的影响程度,获得的最佳超声条件为:固液比1:5,40目,乙醇浓度20%,31℃,28/40kHz双频交变,0.2/0.2W/cm2,浸取35min.浸取浓度26.80mg·mL-1,与预测值的偏差为7.87%,数学模型的有效性较高.     

Anti-nutritional effects of soyabean: a review

Inclusion of raw soyabean in diets considerably inhibits the growth of young animals. This is due to interference with normal gut and systemic metabolism, particularly of pancreas, liver and muscle. Pancreatic hypertrophy and hyperplasia occur in the young of a number of species given soyabean. In the rat, this enlargement, which is primarily a result of interference with CCK-mediated feedback control of exocrine pancreatic secretion, persists upon prolonged feeding and leads to a susceptibility of the pancreas to carcinogens and an increased incidence of neoplasia. In contrast, with pigs or dogs, in which feedback regulation is primarily mediated via secretin, no increase in pancreas enlargement results from consumption of soyabean. Dietary soyabean or trypsin inhibitors do however alter pancreatic secretion in humans. It is at present unclear how this response is mediated. The growth inhibition and interference with intestinal and systemic metabolism observed upon soyabean feeding is due to the presence of trypsin inhibitors, lectin and anti-nutritional factors, devoid of trypsin inhibitory or lectin activity, in the seed meal. The effects of these dietary factors are additive and possibly synergistic. Most of the anti-nutritional effects of soyabean can be abolished by proper aqueous heart-treatment. However, with a proportion of calves, pigs, lambs and humans even heat-treated soyabean has deleterious effects. These can only be eliminated by hot aqueous-ethanol extraction of the meal.     

纸色谱分离-荧光法测定水果(鲜桃)中的胡萝卜素

用纸色谱分离-荧光法对鲜桃中胡萝卜素的测定方法进行了实验研究,通过单因素和正交实验优化鲜桃中胡萝卜素测定方法,确定其最佳条件为:测量波长为448nm、展开剂用量8mL、提取3次、试液的pH=4.5.该方法简单、方便、准确可行.此样品的回收率为99.51%,RSD=1.12%,准确度较高,适用于所有水果和食物中胡萝卜素的测定.     

从红酵母生产水溶性胡萝卜素制品

主要考察了皂化时NaOH浓度，用量、皂化时间及乳化剂的配比和用量等因素对红酵母胡萝卜水溶性和收率的影响，获得了水溶性胡萝卜粉制剂。该制品纯度高，稳定性和水溶性良好，β-胡萝卜素含量为300－800μg/g。     

Growth of Bacillus cereus in soyabean tempeh

Bacillus cereus strains isolated from retail samples of tempeh were added in levels of approx. 10⁵ cfu/g to soaking soyabeans intended for tempeh manufacture. Their growth was prevented and tempeh of good quality was obtained when the soaking resulted in acidification of the beans to pH 4.85, but B. cereus could grow well (approx. 10⁸ cfu/g) in tempeh and cause its spoilage when the soaking did not cause acidification (bean pH 5.70–6.00). Acidification of soyabeans by addition of lactic acid prior to fungal fermentation required pH ≤ 4.4 to prevent B. cereus growth; at this pH, tempeh of good quality was obtained. Acidification of soyabeans with addition of acetic acid inhibited at pH ≤ 5.5 both B. cereus and Rhizopus oligosporus, the mould responsible for tempeh formation; hence, no tempeh could be obtained. Mixed inocula of R. oligosporus and either Lactobacillus plantarum, L. casei ssp. alactosus or L. fermentum produced tempeh of excellent quality. However, mixed inocula containing lactobacilli were not able to prevent B. cereus growth and subsequent spoilage when added to unacidified soyabeans of pH 6.6. This indicates that soyabean acidification, either by biological or by chemical means, is essential to inhibit B. cereus growth during the tempeh fermentation.     

Utilisation,by chicks,of carotene from fresh and dried plant sources

Some factors (autoclaving, addition of ethoxyquin, drying, degree of grinding) influencing utilisation of carotene from plant origin were investigated. Low storage of vitamin A in liver and low excretion of carotene in faeces, when fresh lucerne was given, indicated that carotene-destroying enzymes of plant origin are likely to act before the lucerne is eaten and while it is passing through the intestines. Addition of ethoxyquin to autoclaved lucerne improved the utilisation of carotene. This indicates nonenzymic oxidation of carotene in the digestive tract. Carotene was more effectively utilised from lucerne meal than when given as green lucerne even if autoclaved and with ethoxyquin added. It seems that the influence of non-enzymic factors on the availability of carotene from various dried plants is small and uniform, because carotene was utilised equally from these sources. The particle size (degree of grinding) had no significant influence on the utilisation of carotene from lucerne meal and it seemed that coarser meals could be used without hindering the utilisation of carotene or other carotenoids by chicks.     

葡萄糖-甘氨酸美拉德反应产物对脂肪氧合酶的抑制作用研究

以葡萄糖和甘氨酸为原料制备美拉德反应产物（Glu/Gly-MRPs）,研究其对大豆脂肪氧合酶（LOX）的抑制作用以及机理。结果表明:随着反应中甘氨酸浓度、反应初始pH、反应温度和反应时间的增大,Glu/Gly-MRPs的褐变程度加深,pH下降,对LOX的抑制作用增强;当甘氨酸浓度大于0.6mol/L、反应体系初始pH高于8.0、反应温度高于110℃、反应时间长于3h时,MRPs对LOX的抑制率均趋于稳定值（80%¹00%）。Glu/Gly-MRPs对LOX酶促反应的迟滞时间具有延长作用,通过Lineweaver-Burk双倒数法确定Glu/Gly-MRPs对LOX的抑制类型为混合型抑制。      

胡萝卜色素原料与技术动向

红色在著色剂中是相当有潜力之色素之一。在上市的天色红色素系列中有红麦色素、胭脂红(cochineal)、甜菜根红(beetroot)及花青素(anthocyanin),这些色素因其特性而需考虑色泽、耐热、耐光、耐酸碱及耐蛋白质等种种因素而有用途之限制。例如化青素系的酸性范围具有