Pectolytic Enzymes in Sweet Bell Peppers (Capsicum annuum L.)

Low levels of polygalacturonase (PG) and pectinesterase (PE) activities were quantitated in sweet bell peppers at four stages of maturity based on surface ground color (dark green, light green, turning, and red). The PG activity increased during pepper ripening and was maximal at the turning stage while the PE activity declined during ripening and was maximal at the light green stage. Pepper texture measurements were found to decline concomitantly with the increase in PG activity. Pepper PG showed pH optimum between 4.8 to 5.0 and increased temperature stability with advanced ripening. Compared to tomatoes, pepper PG activity was 116- to 164-fold lower and pepper PE activity was 429- to 1900-fold lower than the corresponding tomato enzymes.     

SOFTENING AND BIOCHEMICAL CHANGES OF SAPOTE MAMEY FRUIT (POUTERIA SAPOTA) AT DIFFERENT DEVELOPMENT AND RIPENING STAGES

We investigated some of the physicochemical and biochemical factors associated with flesh softening of sapote mamey fruit during development and ripening. The activities of pectinmethylesterase (PME), polygalacturonase (PG) and β‐galactosidase (β‐GAL) enzymes were measured in fruits harvested at different development stages, and postharvest in two production seasons. The textural changes were most noticeable at the preclimacteric stage in ripening fruit. The water‐soluble pectin (WSP) increased at a different rate than firmness decreased. No correlation between PG or PME activity and changes in firmness was observed in ripening fruits, though a low correlation was seen between β‐GAL activity and softening in climacteric stage. Greatest loss of firmness occurred in climacteric stage. Fruit pulp softening was not dependent on a single enzyme activity.     

POLYPHENOL OXIDASE FROM BARHEE AND ZAHDI DATES. I. PURIFICATION

Barhee and Zahdi dates (Phoenix dactylifera) contain polyphenol oxidase (PPO) at all maturity stages. The highest PPO activity is present in the medium green and late yellow stages of Barhee and Zahdi dates, respectively. The extracts of medium green stage of Barhee dates contained proteolytic activity. Four PPO forms were purified to homogeneity by acetone precipitation and DEAE-cellulose chromatography. The total fold purification was 8.0, 10.0, 12.5, and 15.0 with 6.7, 0.7, 2.2, and 2.7% recovery of PPO activity. A single PPO form was observed when 1.0mM of phenylmethylsulfonyl chloride (PMSC) was used in extraction solutions. However, only a single PPO form was observed in Zahdi dates and purified 13.1 fold with 7.7% recovery of activity .     

冬枣软化衰老过程中细胞壁酶的活性变化

冬枣果实的软化分为两个阶段。前期下降缓慢,后期加快;低温下PG活性在贮期末呈上升趋势。Cx- cellulase活性变化与PG相似:PME在果实快速软化衰老之前出现活性高峰,可能与快速软化衰老的启动有关。     

Effects of potassium sorbate on postharvest brown rot of stone fruit

The effect of potassium sorbate (K-sorb), a low-toxicity chemical, to control Monilinia spp. was investigated. Preliminary in vitro studies found the MIC of K-sorb for conidial germination and mycelial growth was, respectively, 260 and 1,250 mg/ liter. Immersion of naturally infected peach and nectarine fruit in a solution (15 g/liter) of K-sorb for 120 s reduced brown rot by over 80% in four of five trials. Although treated fruits showed a significant reduction in firmness with respect to the control, they did not reach the overripe stage and retained acceptable quality parameters. In an attempt to elucidate the mechanism of action for K-sorb, the inhibition of enzymatic activity by K-sorb was also tested. In a radial diffusion assay, the addition of K-sorb to agarose reduced polygalacturonase (PG) activity across the concentrations considered. The greatest reduction (54.3%, with respect to the control) was obtained at a sorbate concentration of 15 g/liter. PG kinetic activity of Monilinia laxa observed by a spectrophotometric assay peaked after 40 min in all samples tested. PG activity was significantly higher in the control than in the samples with increased K-sorb concentrations. In conclusion, based on these findings, K-sorb can be recommended as a low-toxicity antifungal compound against Monilinia spp. in peaches and nectarines with its mode of action probably depending in part on the inhibition of PG activity in M. laxa.     

Effects of rumen-protected choline and dry propylene glycol on feed intake and blood parameters for Holstein dairy cows in early lactation

A 6 × 6 Latin square design was used to test 3 sets of comparisons simultaneously to study response in dry matter intake, milk yield, and blood parameters to propylene glycol (PG) supplementation delivered by 2 methods [incorporating PG into the total mixed ration (TMR) vs. top dressing; comparison I]; individual or combined dietary choline and PG supplementation as a 2 × 2 factorial (comparison II); or increasing amounts of dietary choline (comparison III). Six multiparous (lactation number = 1.5 ± 0.8 SD) Holstein dairy cows were at 41 d in milk (± 9 SD) at the start of the experiment. Propylene glycol used was a dry product containing 65% PG, and choline was a rumen-protected choline product (RPC; estimated to be 50% rumen-protected) containing 50% choline chloride. In comparison I, treatments compared were 1) control: no PG; 2) PG-TMR: 250 g/d of dry PG (corresponding to 162.5 g/d of PG) incorporated into the TMR; and 3) PG-top dress: 250 g/d of dry PG top-dressed onto the TMR. In comparison II, treatments compared were 1) control: no PG and no RPC; 2) PG: 250 g/d of dry PG incorporated into the TMR; 3) RPC: 50 g/d of RPC top-dressed onto the TMR; and 4) PG + RPC: combination of treatments 2 and 3. In comparison III, treatments compared were 0, 25, and 50 g/d of RPC top-dressed onto the TMR. Each experimental period lasted 10 d with 9 d of adaptation followed by 1 d of serial blood sampling. Dry matter intake and milk yield were recorded daily. During the serial blood sampling, jugular blood was sampled every 20 min for the first 4 h and at 8 and 12 h after treatment administration. Results obtained from comparison I showed that feeding 250 g/d of PG as a dry product decreased plasma β-hydroxybutyrate (BHBA) concentration (mean ± SEM) from 701 ± 81 (control) to 564 ± 76 μmol/L without affecting serum insulin, plasma glucose, or plasma nonesterified fatty acid concentrations. Top-dressing PG decreased plasma BHBA concentrations more than by incorporating it into the TMR [527 vs. 601 μmol/L (± 81 pooled SEM)]. Results obtained from comparison II showed that supplementing choline as RPC, PG, or both had no effect on dry matter intake, milk yield, or any of the blood parameters measured. Results obtained from comparison III showed that milk yield tended to increase linearly with increasing amounts of dietary choline as RPC. We concluded that feeding PG as a dry product reduced plasma BHBA concentration but top-dressing PG was more efficient at reducing plasma BHBA level than incorporating PG into the TMR. Dietary choline as RPC tended to increase milk yield linearly. However, a combined effect of dietary PG and choline was not evident and therefore not beneficial.     

Ruminal and blood responses to propylene glycol during frequent feeding

The objective of the current experiment was to study the responses of ruminal and blood metabolites of Holstein dairy cows to propylene glycol (PG) under different methods of delivery during frequent feeding. By providing the same amount (200 mL or 200 g) of PG, delivery methods for PG were assessed: 1) control treatment: no PG; 2) dietary treatment: 200 g of PG as a dry product (65% purity; corresponded to 308 g of the dry product) mixed into the TMR; 3) oral-drench treatment: 200 mL of liquid PG (100% purity) orally drenched; and 4) rumen-drench treatment: 200 g of PG as a dry product drenched via the rumen cannula to mimic top dressing. Eight multiparous (lactation = 3 ± 1.1 SD) ruminally cannulated Holstein dairy cows (DIM = 204 ± 104.5 SD) were fed PG for 4 d (d 11 to 14) in a replicated 4 × 4 Latin square design with an experimental length of 14 d for each period. On the last day of each period, serial blood samples were removed from an indwelling catheter placed in the right jugular vein immediately before and for 4 h after PG administration. Cows were fed at 12× feeding/d for 2 d before entering the serial sampling period to minimize postprandial influences on blood metabolites. Ruminal content was also sampled hourly for 4 h on d 14. Milk was sampled from 2 consecutive milkings on d 13 during each period. Dry matter intake and milk yield were not affected by PG. Percentages of milk lactose were increased by PG delivered by all methods tested in the current experiment. Ruminal concentrations (as percentages of total volatile fatty acids) of acetate were decreased and concentrations of propionate and isovalerate were increased by PG, regardless of the delivery method; however, total volatile fatty acid concentration was not affected by PG. Ruminal concentrations of butyrate were decreased and concentrations of valerate were increased by PG drench, via either an oral or ruminal drench. The degree of reduction in butyrate concentration or increase in valerate concentration was affected by PG dose. Serum insulin peaked more rapidly and at a greater concentration for cows receiving PG via drenching, but not when PG was provided as a part of the TMR. Plasma glucose, however, tended to peak more rapidly at a greater concentration for cows receiving PG, regardless of the delivery method. Propylene glycol for the amount drenched (orally or ruminally) or fed (incorporated into the ration) shifted ruminal fermentation toward a more glucogenic environment. Drenching demonstrated a better efficacy than feeding PG because of the amount of PG that was available to the animal at the time of sampling. Effects of drenching dry PG into the rumen were comparable with orally drenching liquid PG.     

The composition of maturing Omani dates

The composition of two varieties of Omani dates, fard and khalas, was determined as maturity progressed. Free sugars and dietary fibre content were examined in detail. High-performance liquid chromatography (HPLC) of the extracts showed that at the early green stage (Arabic kimri), dates contained small amounts of glucose and fructose. At the intermediate yellow (khalal) and red (rutab) stages, large amounts (500–565 g kg⁻¹ dry weight) of sucrose had accumulated, but no additional glucose or fructose was detected. At the final mature (tamar) stage, all sucrose was converted to glucose and fructose (>800 g kg⁻¹ dry weight). Dietary fibre, determined as non-starch polysaccharides (NSPs) by gas chromatography (GC), decreased from 250 g kg⁻¹ (kimri) to 50 g kg⁻¹ (tamar) on a dry weight basis. The principal monomers of NSPs were glucose, galactose, xylose, mannose, arabinose and rhamnose. On a dry weight basis, pectin, protein and ash contents decreased as the dates matured. On a fresh weight basis, changes in NSPs, pectin, protein and ash could be attributed to loss of moisture and the accumulation of sucrose initially, or of invert sugar later as maturation progressed. © 1999 Society of Chemical Industry     

热与超声波对多聚半乳糖醛酸酶的钝化动力学

以多聚半乳糖醛酸酶（polygalacturonase,PG）为研究对象,探讨了在热与超声波作用下PG的钝化动力学。采用3,5-二硝基水杨酸比色法测定酶活力。结果表明：单独的热（≤45 ℃）或超声波（频率20 kHz,温度0 ℃,功率密度242、605、968 W/cm2）处理对PG钝化作用不明显,残留活力均在80%以上,并且处理15 min后,酶活力基本不变,动力学符合部分转化模型。但两者同时处理能使PG显著失活,钝化效果符合一级动力学模型。在20 kHz、35 ℃、605 W/cm2条件下处理16 min可使酶活力降至13.72%。先进行热处理（35 ℃、5 min）再进行超声波处理（0 ℃、605 W/cm2、0～10 min）或先进行超声波处理（0 ℃、605 W/cm2、5 min）再进行热处理（35 ℃、0～10 min）均不能有效钝化PG,表明只有在两者同时作用的前提下,才能表现出协同效应,达到更好的钝酶效果。PG是影响果蔬汁品质的主要酶之一,本实验不仅为超声波钝化PG提供了理论数据,也为果蔬汁加工提供了研究参考。     

Structural and chemical differences in the cell wall regions in relation to scale firmness of three onion (Allium cepa L.) selections at harvest and during storage

BACKGROUND: Firmness in vegetables is an important textural attribute affecting consumer attitudes toward freshness and quality. Firmness, structural carbohydrates, polygalacturonase (PG), and pectin methylesterase (PME) activity were measured in three onion (Allium cepa L.) lines at harvest and after 4, 8, and 12 weeks of storage. RESULTS: The high‐dry‐matter onion, MBL87‐WOPL, had the firmest bulbs at harvest and delayed softening during storage. MBL87‐WOPL had the thickest cell wall/middle lamella region, and highest levels of dry matter and total uronic acid. Furthermore, MBL87‐WOPL had the lowest levels of PG and PME activity during storage. Pegasus, a poor‐storing cultivar, had the softest bulbs at harvest, lowest levels of uronic acid, and thinnest cell wall/middle lamella. A good storing, moderately firm onion cultivar (MSU4535B) presented intermediate levels of firmness and total uronic acid content. Differences in uronic acid in water‐soluble pectin accounted for much of the difference in total uronic acid among lines. Cellulose concentrations were similar among all lines at harvest. In addition, cellulose concentrations decreased in all lines during storage. Transmission electron microscopy performed on bulbs at harvest and after 12 weeks of storage indicated that degradation of the middle lamella had occurred during storage, leading to cell separation. CONCLUSION: Our results suggest that differences in onion scale firmness at harvest may be due to differences in water‐soluble pectin uronic acid concentrations. Furthermore, the rate of bulb softening during storage at 6.6 °C was greater in onion lines with higher levels of PME and PG activity in storage. Copyright © 2008 Society of Chemical Industry     

胡椒经地衣芽孢杆菌发酵脱皮过程中的主要酶系及pH值变化

采用地衣芽孢杆菌进行静置液态发酵对胡椒进行脱皮,与生产实践中传统水沤法脱皮对比,研究二者发酵脱皮过程中的果胶酶、木聚糖酶、纤维素酶和发酵液pH值的动态变化。结果表明：在发酵脱皮过程中,两种方法的聚半乳糖醛酸酶(PG)和果胶裂解酶(PL)变化规律相似,都出现两次酶活力高峰;而纤维素酶活力都很低,果胶酯酶(PE)酶活力都比较高;在传统水沤法中木聚糖酶活力出现两个高峰,而在发酵法中木聚糖酶活力在脱皮后期逐渐上升;pH值变化总趋势也相似,脱皮完成时pH值均在5～5.5之间。由此推知,胡椒鲜果发酵脱皮过程中果胶酶系起主要作用,脱皮前期PG、PL先作用于果胶类物质,破坏胶质复合体的稳定结构,PE再作用于果胶分子,形成果胶酸,同时pH值降低,脱皮后期木聚糖酶活力上升,半纤维素降解加快,在多种酶的协同作用下,胡椒鲜果最终完成彻底脱皮。     

蜂胶在食用油脂中的抗氧化作用

本文以猪油、菜油为实验材料,测定其POV值来评价蜂胶在动物油和植物油中的抗氧化特性,并与没食子酸丙酯(PG)比较.结果表明蜂胶能够延缓这些底物的氧化进程,明显延长诱导期.且柠檬酸、卵磷脂能增强其抗氧化功能.蜂胶的抗氧化能力强于相近浓度的PG,蜂胶在短时间高温加热后,其抗氧化效率不受影响.     

Small Grains for Forage

Two cultivars each of four species of cereals were harvested at head, milk, and dough stage. In each of 2 yr the yield and content of DM, NDF, and ADF, lignin, CP, and in vitro DM disappearance were quantified. There were large differences in yield and chemical composition due to year, species, and harvest date. Yield varied from a low of 3.0 metric tons dry matter per hectare for Norwin barley at head stage in the 1st yr to a high of 10.6 for Mariner oats at milk stage in the 2nd yr. Overall average yield was 6.6 with yearly averages of 5.4 and 7.8 metric tons of DM per hectare. Dry matter yield increased as the crop matured, averaging 4.8, 7.4, and 7.6 metric tons per hectare at the three successive harvest dates. Fiber and lignin increased with each harvest date but CP decreased from 13.6 to 8.1% and in vitro DM disappearance decreased from 66 to 56%. Differences among cultivars and species allow forages to be chosen that will be suitable for various animal species and available on calendar dates needed.     

QUALITY ATTRIBUTES, PECTOLYTIC ENZYME ACTIVITIES AND PHYSIOLOGICAL CHANGES DURING POSTHARVEST RIPENING OF NECTARINE

The postharvest ripening at 20C and 90–95% RH for 10 days of ‘Armking’ nectarine grown in a greenhouse was investigated over two seasons. Firmness, titratable acidity, ascorbic acid, pH and maturity index were all adequate to stablish the rate of ripening. However, soluble solids content and reducing and non-reducing sugars showed no significant changes. It took about 10 days for very early ripening fruit (100 g weight and 82 N firmness) and 6 days for normal early ripening fruits (115 g weight and 46 N firmness), both harvested at preclimacteric stage, to become eating ripe (near 20 N). Total weight loss and decay after 10 days was approximately 11%. During ripening there was a temporal coincidence among higher rates of ethyleneproduction, higher pectinmethylesterase (PME) and polygalacturonase (PG) activities, lower firmness and acidity and higher maturity index. PME and PG activities increased during ripening, with a highly negative linear correlation between activities of the two enzymes and firmness. In very early ripening fruit, PME activity was more closely related to softening than PG, whereas in normal early ripeningfruit, PG activity was slightly more closely linked to the loss offirmness than PME.     

天然保鲜剂涂膜处理对弥猴桃采后软化效果的影响

以“金魁”美味猕猴桃为试材,对2种保鲜剂在猕猴桃贮藏过程中的作用机理进行了探讨。结果表明,水杨酸处理能抑制猕猴桃淀粉酶活性,延缓第1阶段的软化,壳聚糖处理对猕猴桃贮藏过程中果胶酶的活性有较强的抑制作用,能延缓第2阶段的软化,壳聚糖处理对猕猴桃整个软化过程的抑制作用优于水杨酸处理。     

番茄浆保温处理的工艺研究

以番茄为原料,研究了保温处理对番茄浆液果胶酶和果胶物质含量等指标的影响。结果表明:保温处理对番茄浆液的可溶性固形物和色泽的影响不明显,果胶含量随着保温温度升高、时间延长和pH增大均呈先上升后下降的趋势;果胶酶活性随着保温温度升高、时间延长和pH增大呈先升高后降低的趋势;原果胶含量随着保温温度升高、时间延长和pH增大均呈先下降后上升的趋势。番茄浆液(pH自然)在50℃水浴中保温2h后灭酶,生成的果胶量最多。     

木枣多糖的理化特性研究

为充分利用红枣资源,挖掘不同采收期枣果的加工利用价值,以木枣为试材,对比分析白熟期、半红期、全红期三个采收期木枣经自然晾干、热风干燥、真空冷冻干燥后营养、色泽、质地品质指标的变化。结果表明：相同干制方式下白熟期木枣V_C、粗纤维、黄酮、三萜类化合物的含量高于半红期,半红期的高于全红期;白熟期木枣可溶性糖和多糖含量显著（P<0.05）低于半红期,半红期的显著（P<0.05）低于全红期;除了可溶性糖外,三个采收期木枣真空冷冻干燥后营养功能成分含量最高,但白熟期和半红期木枣自然晾干或热风干燥后可获得较全红期枣果真空冷冻干燥后高的粗纤维、黄酮、三萜类化合物含量。三个采收期木枣果肉颜色均为绿白色,白熟期木枣质地相对偏硬,半红期和全红期没有显著（P>0.05）差异,真空冷冻干燥较好的保持了木枣原有的色泽品质和质构特性,而自然晾干和热风干燥则促使白熟期和半红期木枣果皮果肉均由绿转红,色差增大,硬度升高,接近甚至高于全红期木枣。由此可得,提前采收的白熟期和半红期木枣具备较好的加工利用特性,真空冷冻干燥为木枣高值化加工的首选干燥方法。研究结果为木枣提前采收加工利用提供了理论依据。     

15-Hydroxyprostaglandin dehydrogenase in the bovine endometrium during the oestrous cycle and early pregnancy

Prostaglandins (PG) are primary regulators of reproductive function. In ruminants, the relative production of PGE2 and PGF2alpha determines the return to a new oestrous cycle or to the establishment of pregnancy in response to a viable embryo. PG action depends on biosynthesis, transport and interaction with their receptors, which are all expressed differentially during the oestrous cycle. PGs are, however, local mediators and thus the onsite degradation by enzymes such as 15-hydroxyprostaglandin dehydrogenase (HPGD), also known as 15-PGDH, is another factor to consider in the regulation of physiological action. Little information is available on PG catabolism in the endometrium during the oestrous cycle or early pregnancy. The purpose of this study was to clone the bovine 15-PGDH, produce the recombinant protein and generate a specific antibody to study its activity and its expression in the endometrium during the oestrous cycle. We have found that the bovine 15-PGDH is highly homologous to the rat and human isoforms. 15-PGDH is localized principally in the glandular epithelium and to a lesser extent in stromal and luminal epithelial cells. The enzyme expression is regulated during the oestrous cycle and it reaches its maximal level on days 16-18. Transient expression is observed in luminal epithelial and trophoblast cells on day 21 of pregnancy. The mRNA is expressed at a constant high level throughout the cycle. The activity of the recombinant 15-PGDH was also tested and was found comparable for PGF2alpha and PGE2. These data suggest that 15-PGDH contributes to the tight regulation of PG action in the endometrium especially at the critical period of recognition of pregnancy.     

Respiration,pectolytic activity and textural changes in ripening African mango (Irvingia gabonensis) fruits

Post-harvest changes in fruit firmness, respiration, pectinesterase (PE) and polygalacturonase (PG) activities were followed in African mango fruits during storage ripening at tropical ambient conditions (28±1°C and 68±2% RH). Respiration followed a climacteric pattern attaining a peak of 99·37 ml CO₂ kg^?1 hr^?1 on the fifth day of storage while full ripeness (colour index—5) was attained on the tenth day. PE and PG activities increased with progressive fruit ripening attaining their optima on the fifth day (1·8 PE unit) and tenth day (27 PG units), respectively. Fruit firmness decreased as pectolytic activity increased with a concomitant reduction in the deformation force from 49 kPa in the unripe fruit to 25 kPa at the edible ripe stage.