吉林晒烟多酚类物质及其相关酶活性的变化动态

选取吉林当地3个主栽晒烟品种研究了不同晒烟品种叶片发育过程中多酚类物质及其相关酶活性的动态变化以及两者之间的关系。结果表明,不同晒烟品种中总酚含量表现为青黄叶＞大叶黄＞大白花,总酚在整个生育期的含量为0.16%~1.2%。不同晒烟品种中总酚含量随着叶龄的增加而提高,在成熟期稍有降低;青黄叶和大叶黄中绿原酸、芸香苷和莨菪亭在叶片发育过程中整体上表现出上升趋势,而大白花中绿原酸、芸香苷和莨菪亭含量呈单峰曲线。各品种中苯丙氨酸解氨酶活性与绿原酸和芸香苷的变化规律相同,多酚氧化酶活性和过氧化物酶活性呈单峰趋势。在烟叶生长过程中,各晒烟品种中苯丙氨酸解氨酶活性与绿原酸、芸香苷、莨菪亭和总酚的变化呈正相关,且与绿原酸和芸香苷达到显著水平;多酚氧化酶活性变化与绿原酸、芸香苷、莨菪葶和总酚的相关性表现为负相关,但未达到显著水平;过氧化物酶活性与绿原酸、芸香苷、莨菪葶和总酚呈正相关,且与总酚达显著水平。由此可见,苯丙氨酸解氨酶和过氧化物酶与多酚类物质之间有显著的相关性,可以通过调节这两种酶的活性来控制多酚的含量,从而改善烟叶质量。     

Effects of heat treatment on the quality of fresh-cut Chinese water chestnut

A heat treatment to inhibit browning and maintain the quality of fresh‐cut Chinese water chestnut was developed. Slices of Chinese water chestnut, cv. Guilin, were immersed in boiling water for 30 s, placed into film‐wrapped trays and then stored at 4 °C for up to 12 days. Changes in browning, eating quality and disease incidence were measured. The effect of heat treatment on the content of total phenolics and activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) was also evaluated. The heat treatment effectively prevented browning associated with PAL, PPO and POD activities and total phenolic content and delayed the decrease in eating quality, which is associated with reduced total soluble solids, titratable acidity and ascorbic acid, compared with fresh‐cut Chinese water chestnut. Inhibition of browning by heat treatment without microbial growth was achieved for 12 days of storage at 4 °C. These results showed that heat treatment effectively maintained the quality of fresh‐cut Chinese water chestnut.     

温度对黄皮果实PAL、POD和PPO活性的影响

为探明贮藏过程中温度对黄皮果实采后保鲜的效果,研究了2～4℃、6～8℃和10～12℃等不同贮藏温度对黄皮果实几种酶活性的影响。结果表明,贮藏温度在2～12℃时,贮藏温度越低,保鲜效果越好,适宜的贮藏温度为2～4℃。2～4℃贮藏的黄皮果实苯丙氨酸解氨酶(PAL)活性高于6～8℃和10～12℃贮藏的果实,而过氧化物酶(POD)和多酚化物酶(PPO)活性低于6～8℃和10～12℃贮藏的果实。2～4℃贮藏能增强黄皮果实的防伤害能力,明显抑制黄皮的酶促反应,有利于贮藏期限的延长。     

Polyphenol oxidase activity in white tan‐plant‐type sorghums: An important determinant of the relatively dark colour of their porridges

The relatively dark colour of food products from white tan‐plant (food‐grade) sorghums can compromise their acceptability. The relationship between white tan‐plant sorghum polyphenol oxidase activity (PPO) and porridge colour was investigated, primarily using lines grown in the same locality over two seasons. Sorghum was intermediate in PPO between wheat and maize. White tan‐plant sorghum and white maize whole grain flours were similar in colour. However, with white tan‐plant sorghum, the transition from flour to porridge caused a much larger reduction in L* value. Further, the correlation between white tan‐plant sorghum PPO activity and porridge L* values was highly significantly negative (P < 0.001), the relationship accounting for 40–50% of variation. PPO in white tan‐plant‐type sorghums is therefore an important determinant of the relatively dark colour of porridges. Breeding to reduce PPO activity could improve consumer appeal. Cultivar Sima (IS 23520) that had low PPO activity and produced light‐coloured porridge could be useful for breeding.     

Reassessment of treatments to retard browning of fresh‐cut Russet potato with emphasis on controlled atmospheres and low concentrations of bisulphite

The cultivar Pacific Russet with high browning susceptibility was used for most testing. Controlled atmospheres (0.3%, 3% and 21% O₂ in combination with 0%, 6% or 12% CO₂) and anti‐browning chemicals were studied in relation to quality retention and wound‐induced phenolic metabolism of fresh‐cut slices for up to 16 days at 5 °C. The 3% O₂+ 12% CO₂ atmosphere was most effective among those tested, and retarded increases in phenolics and phenylalanine ammonia lyase activity, but had only slight benefit on visual quality. A 1.25% ascorbic acid +1.25% citric acid treatment was ineffective, but when combined with 3% O₂+ 12% CO₂, it was comparable with 0.025% sodium bisulphite. Bisulphite concentrations from 0.05% to 0.25% provided similar effective control of discolouration. Bisulphite as low as 0.025% with 3% O₂+ 12% CO₂ resulted in a visual quality score at the limit of marketability after 8 days at 5 °C. Chemical treatments did not retard increases in phenolic concentrations or phenolic enzyme activities.     

The effect of germination and kilning on the cyanogenic potential,amylase and alcohol levels of sorghum malts used for burukutu production

Grain sorghum of the red and white varieties was malted by steeping in water for 18 h, germinated over 5 days and kilned at 50 °C. The malts were analysed for amylase activities and cyanogenic potential and used to produce burukutu, an alcoholic beverage. The alcohol content of the burukutu was recovered by distillation and determined by the refractive index method. α‐Amylase activity peaked on malting day 3 and was higher in the white malts. β‐Amylase activity peaked on day 3 in the red malts and on day 4 in the white malts, but was higher in the red malts. Dhurrinase activity was highest on malting day 4, with a higher activity in the red malts. Kilning at 50 °C reduced the activities of these enzymes. The dhurrin content increased during germination and was consistently higher in the white malts, in which there was evidence of dhurrin mobilisation. In the red malts the dhurrin content increased during germination but decreased progressively after kilning; evidence of dhurrin mobilisation was apparent as from malting day 4. Burukutu produced from the red malts gave higher alcohol contents than that from the white malts. Maximum alcohol yields were obtained on malting day 3 in the red malts and on day 5 in the white malts. © 2000 Society of Chemical Industry     

Effect of thermal processing on oxide reductase inactivation and on colour fixing in erva‐mate (Ilex paraguariensis St. Hill) leaves

Leaves of erva‐mate (Ilex paraguariensis St. Hill) were heat treated with different combinations of time and temperature. Polyphenol oxidase (PPO) and peroxidase (POD) residual activities and colouring (L, a, b and ΔE) were studied after treatment for 3 weeks. The best results for enzyme inactivation after heat treatment were obtained with the leaves treated at 450 °C for 15 s and at 500 °C for 10 s, with reductions of 90.6% and 83.4% for PPO and 94.5% and 92.7% for POD. These groups also showed low levels of enzyme activity during the first few days of storage, and a few days later no enzyme activity was detected. The data on the colours, specially –a values (green colour), were in accordance with results for enzyme activity and helped in the research on the changes that occur in the leaves during storage. Data from this work can be suggested for the improvement of the current method of erva‐mate processing, which is still performed empirically.     

The effect of sorghum type and processing on the antioxidant properties of African sorghum-based foods

This work determined the effect of sorghum type and different processing technologies of traditional African sorghum foods on total phenols, tannin content and antioxidant activity. The products were prepared by fermentation, conventional and extrusion cooking of whole and decorticated ground grain. The tannin sorghum types, had higher ABTS and DPPH antioxidant activities, compared to the types without tannins. Antioxidant activity was significantly correlated with total phenols and tannins (r > 0.95). Decortication, reduced antioxidant activity of both tannin and non-tannin sorghum by 82–83% due to the removal of the pericarp and the testa, which decreased phenols. Processing, generally decreased antioxidant activity, however, conventionally cooked porridges had higher antioxidant activity than the extrusion cooked products. The retention of antioxidant activity, particularly in fermented and unfermented porridges, means that whole tannin sorghum can be processed into foods with potential health benefits.     

Effects of catechin on the phenolic content and antioxidant properties of low‐fat cheese

The effect of (+)‐catechin on total phenolic content (TPC) and antioxidant properties in low‐fat hard cheese were examined over a 90‐day ripening period at 8 °C. Antioxidant activity (AA) in cheese was measured by ferric reducing antioxidant power, oxygen radical absorbance capacity (ORAC) and 2,2‐diphenyl‐1‐picrylhydrazyl assays and compared with TPC. Catechin retention coefficients in cheese curds were in the range of 0.63–0.75 and decreased the pH of cheese without affecting protein, fat or moisture content. Both TPC and AA increased during the 90‐day ripening period. Oxygen radical absorbance capacity was the most suitable technique for evaluating AA in cheese due to the high correlation with TPC and suitability in both lipophilic and hydrophilic systems.     

Application of the dual attribute time‐intensity (DATI) sensory method to the temporal measurement of bitterness and astringency in sorghum

Bitterness and astringency are attributes generally cited as the cause of tannin sorghums being unpalatable. The objective here was to determine the effect of sorghums with varying tannin content on bitterness and astringency simultaneously using dual attribute time‐intensity (DATI). A trained panel assessed bitterness and astringency of bran infusions of tannin and tannin‐free sorghums. In both sorghum types, bitterness developed and reached maximum intensity faster (T_max 22.5 s; P < 0.001) than astringency (27.9 s). The duration of the astringent sensation (D_tot 69.9 s) lasted longer than bitterness (66.3 s). Overall, the temporal parameters for bitterness distinguished infusions from tannin and tannin‐free sorghums slightly more clearly than those for astringency. The research established that, for sorghum, bitterness and astringency are related. The DATI method also revealed that panellists’ perceptions of the time course of bitterness and astringency differ.     

Impact of germination on the chemical components and bioactive properties of adlay (Coix lachryma‐jobi L.) water extract

In recent years, adlay water extract and related products have been widely consumed. This study investigated the chemical components and bioactive properties of adlay water extract at different germination stages. Glucose and maltose were significantly increased, whereas fructose was slightly decreased after germination. The contents of vitamins C and B₁ in the water extract increased 1.61‐ and 2.68‐fold, respectively. The amounts of peptides, especially those with a molecular weight under 3000 Da, were significantly increased after germination. During germination, the level of total free amino acids rose from 54.09 to 128.22 μg mL^?1, and the percentage of essential amino acids was elevated from 21.63% to 42.13%. Germination also substantially augmented the total phenolic content and antioxidant activity of the water extract. Moreover, the germinated adlay water extract showed higher inhibitory activity on angiotensin‐converting enzyme (ACE), xanthine oxidase and tyrosinase than the water extract of nongerminated adlay. These findings revealed that germination might be a potential way to improve the nutritional value and bioactive properties of adlay water extract.     

Reactions with phenolic substances can induce changes in some physico-chemical properties and activities of bromelain – the consequences for supplementary food products

Bromelain was allowed to react with phenolic compounds. The activity and selected physico‐chemical properties of the resulting derivatives were characterized. In vitro experiments showed that the proteolytic activity of bromelain was inhibited. Bromelain also serves as a food protein, because food stuffs based on pineapple contain relatively high concentrations of bromelain. In vitro digestion of bromelain derivatives with the main proteolytic enzymes of the gastrointestinal tract was also adversely affected. A covalent attachment of the phenolic compounds was identified at the tryptophan, free amino (lysines and N‐terminal) and thiol groups of bromelain. A decrease in solubility of the derivatives was observed. The isoelectric point was shifted to lower pH values and high molecular weight fractions were identified. All effects observed depended on the reactivity of the phenolic substances. Two supplementary food products containing both bromelain and quercetin were also tested in terms of their proteolytic activity and digestibility.     

Effects of a mixed koji culture of Aspergillus oryzae HG‐26 and Aspergillus niger HG‐35 on the levels of enzymes,antioxidants and phenolic compounds in soy sauce during the fermentation process

Soy sauce contains a number of bioactive components, which have been shown to possess strong antioxidative properties. The objective of this study was to compare the enzyme activities, antioxidant activity and phenolic compounds content of soy sauces prepared from a mixed koji (SSAON, inoculated with Aspergillus oryzae HG‐26 and Aspergillus niger HG‐35), with those of soy sauces made from a koji culture containing only Aspergillus oryzae HG‐26 koji (SSAO). The total phenolic content (TPC), total flavonoid content (TFC), content of three isoflavone aglycones (daizein, glycitein and genistein) and the antioxidant activity of the SSAON were found to be higher than those of the SSAO during moromi fermentation. In addition, they showed strong positive correlations with the antioxidant potential of the soy sauce. This study has demonstrated the potential of a mixed‐culture koji, based upon A. orzyae and A. niger, for the production of soy sauce with an increased level of bioactive components.     

Effects of different osmo‐dehydrofreezing treatments on the volatile compounds,phenolic compounds and physicochemical properties in mango (Mangifera indica L.)

The influences of different osmotic solution pretreatments (sucrose, glucose and maltose with concentration of 45%) on the volatile compounds, phenolic compounds and other physicochemical parameters in frozen mangoes were studied. Volatile and phenolic compounds were measured using SPME/GC‐MS and HPLC method, respectively. The results revealed that compared with untreated frozen mango, some volatile compounds (e.g. alcohols, aldehydes and some terpenes and esters) increased significantly and there were more compounds identified in osmo‐dehydrofrozen samples. These changes positively affected mango aroma and resulted in higher sensory scores for osmo‐dehydrofrozen samples. In addition, data on phenolic compounds showed that dehydrofrozen samples pretreated in glucose and sucrose had higher ρ‐hydroxybenzoic acid and quercetin contents, respectively, while samples pretreated in maltose showed higher ρ‐coumaric acid and sinapic acid contents compared with untreated frozen samples. The current work indicates that osmo‐dehydrofreezing can improve the retention of phenolic and aromatic compounds in frozen mango.     

Effect of acid hydrolysis in the presence of anhydrous alcohols on the structure,thermal and pasting properties of normal,waxy and high‐amylose maize starches

Maize starches with different amylose contents (0%, 23% and 55%) were treated in anhydrous methanol, ethanol, 2‐propanol, 1‐butanol with 0.36% HCl at 25 °C for 5 days. Results showed that the extent of change in physicochemical properties increased from methanol to butanol. Treated waxy maize starch showed higher than 65% solubility at above 75 °C. The diffraction peak at 2θ = 5.3° of amylomaize V starch disappeared after treatment in ethanol, 2‐propanol and 1‐butanol. Acid–alcohol treatment decreased the gelatinisation temperature of normal (from 64.5 to 61.9 °C) and waxy maize (from 68.1 to 61.1 °C) starches, while it increased that of amylomaize V (from 68.7 to 72.3 °C) starch. The extent of the decrease in the pasting viscosity followed the following order: amylomaize V < normal maize < waxy maize. This study indicated that acid–alcohol treatment degraded preferentially the amorphous regions and the different changes depended on the crystal structure and amylose content of starch.     

Integration of ileum cannulated pigs and in vitro fermentation to quantify the effect of diet composition on the amount of short‐chain fatty acids available from fermentation in the large intestine

Using cannulated pigs and a standardised in vitro fermentation system the effect of diet and non‐starch polysaccharides (NSP) on the amount of energy available from microbial fermentation in the large intestine could be predicted. The available energy was calculated from the amounts of short‐chain fatty acids (SCFA) produced. Three diets were investigated: a low fibre diet based essentially on wheat flour (56 g NSP kg⁻¹ feed) and two high fibre diets with added oat bran (93 g NSP kg⁻¹ feed) or wheat bran (102 g NSP kg⁻¹ feed). Colonic fermentation was estimated by in vitro fermentation of freeze‐dried ileal effluent collected from cannulated pigs. The in vitro fermentation method was optimised to use 10 g ileum content litre⁻¹ incubated at pH 6.0 in a fermentor containing faecal slurry consisting of anaerobic mineral salts medium and 50 g litre ⁻¹ faeces from pigs fed the same diets as the cannulated pigs. The results demonstrate that it is very important to compensate for the faecal SCFA contribution when calculating the amount of SCFA produced from ileal digesta during in vitro fermentation. The amount of NSP digested in vitro was compared with data obtained from in vivo studies and there was a good agreement between in vivo and in vitro data. We concluded that the integrated in vivo–in vitro method is a valuable technique to estimate the effect of diet and NSP on the amount of SCFA produced in the large intestine and when fed the three diets the microbial fermentation in the large intestine provided between 2.4–6.4% of the total available energy. © 1999 Society of Chemical Industry