Enzymatic changes in pectic polysaccharides related to the beneficial effect of soaking on bean cooking time

BACKGROUND: Cooking time decreases when beans are soaked first. However, the molecular basis of this decrease remains unclear. To determine the mechanisms involved, changes in both pectic polysaccharides and cell wall enzymes were monitored during soaking. Two cultivars and one breeding line were studied. RESULTS: Soaking increased the activity of the cell wall enzymes rhamnogalacturonase, galactanase and polygalacturonase. Their activity in the cell wall was detected as changes in chemical composition of pectic polysaccharides. Rhamnose content decreased but galactose and uronic acid contents increased in the polysaccharides of soaked beans. A decrease in the average molecular weight of the pectin fraction was induced during soaking. The decrease in rhamnose and the polygalacturonase activity were associated (r = 0.933, P = 0.01, and r = 0.725, P = 0.01, respectively) with shorter cooking time after soaking. CONCLUSION: Pectic cell wall enzymes are responsible for the changes in rhamnogalacturonan I and polygalacturonan induced during soaking and constitute the biochemical factors that give bean cell walls new polysaccharide arrangements. Rhamnogalacturonan I is dispersed throughout the entire cell wall and interacts with cellulose and hemicellulose fibres, resulting in a higher rate of pectic polysaccharide thermosolubility and, therefore, a shorter cooking time. Copyright © 2011 Society of Chemical Industry     

间歇升温处理对油豆角贮藏期间冷害的控制研究

以吉林特产油豆角为试材,研究油豆角0℃冷胁迫处理间歇升温对冷害的回避效果。结果表明:油豆角0℃处理20d即出现典型水浸状冷害症状,间歇升温至4、8℃和室温(20～25℃)处理,均可有效地减缓冷害症状。其中间歇升温至8℃对冷害的回避作用最为显著,呼吸高峰较对照组推迟10d出现,贮藏35d后,冷害指数、细胞膜透性、MDA含量分别比对照组低33%、29.13%、14.06nmol/g·FW,多酚氧化酶活性升高了0.73U;升温至4℃处理效果没有升温至8℃显著;升至室温处理,前期对冷害症状有所缓解,但后期冷害加剧,褐变反而严重。      

Color changes during storage of honeys in relation to their composition and initial color

The causes of darkening in honey have been attributed to Maillard reaction, fructose caramelization and reactions of polyphenols, however, no systematic studies exist on this subject. The influence of composition and initial color on the rate of darkening of several Argentine honeys submitted to storage at 37°C during 90 days was evaluated through spectrocolorimetric measurements. The most suitable color functions to evaluate darkening of honeys [lightness (L_ab*), browning index (BI), metric chroma (C_ab*), metric hue (H_ab*) and 1/Z] increased linearly as storage time increased, after an initial induction period of very low browning development. The slope of the linear browning development zone with time was an index of browning rate, and it was analyzed in relation to the initial color and the composition of honeys (moisture content, total nitrogen, total lipids and polyunsaturated fatty acids, fructose and glucose content). Of the analyzed variables, the initial color was the parameter which better defined the rate of darkening of honeys.     

The stability of vitamin A in fortified palm olein during extended storage and thermal treatment

The stability of vitamin A in Refined Bleached Deodorised Palm Olein (RBDPOL) was studied for 24 months. Vitamin A decreased with time, temperature and thermal treatment (frying/cooking). RBDPOL fortification was observed over several temperature ranges, using PET, nylon and HDPE commercial packaging materials. After 24 months, the following vitamin A contents of 39–43 IU g^?1 (39–45%) at 16–20 °C; 35–40 IU g^?1 (43–49%) at 24–29 °C; and 28–39 IU g^?1 (45–73%) at 24–45 °C were detected at the respective temperature ranges. Results showed stability of vitamin A fortified RBDPOL vegetable oil was not stable over typical shelf life (12 months). Depletion of vitamin A accelerated when the RBDPOL vegetable oil was subjected to high temperature thermal treatment.     

Deoxynivalenol and ochratoxin A in German wheat and changes of level in relation to storage parameters

The occurrence of the mycotoxins deoxynivalenol (DON) and ochratoxin A (OTA) in the winter wheat of 1997 and 1998 grown under organic farming conditions was investigated using ELISAs (R-Biopharm®) for quantification. The influence of delayed drying of the grain after harvest on the development of DON and OTA was determined in storage trials (moisture: 17% and 20%; temperature: 20°C; duration: four and six weeks). The Tox5 PCR assay was used both to detect Fusarium species with the potential to produce trichothecenes and as a measure of their relative DNA content during the storage trials. The intensity of the PCR signals was correlated with the DON concentration. Fusarium species were identified microscopically by standard methods. All the freshly harvested grain samples were contaminated with DON and showed further increases in the DON concentration during storage. OTA contamination was found in 14.3% of the 1997 samples and in 24.1% of the 1998 samples. OTA increased during storage trials of the 1997 samples but not in the 1998 samples.     

Changes in some nutritional,bioactive and morpho-physiological properties of common bean depending on cold storage and seed moisture contents

Seed moisture content is one of the most important storage parameters affecting the quality of stored common beans. This study was conducted to investigate the changes in some nutritional, bioactive and morpho-physiological properties of common bean stored at three different seed moisture contents (6.4, 11.7 and 17.3%), 4 °C and 65% RH for 12 months. Significant differences were determined in terms of examined properties depending on different seed moisture contents before and after storage. Protein, essential mineral contents, total phenolic content, bulk density, true density and electrical conductivity decreased consistently as seed moisture content increases both before and after storage. On the contrary, dimensional properties, shape index values, thousand grain weight and total flavonoid content increased linearly with increase of seed moisture content both before and after storage. As a result, protein, essential mineral contents (potassium, magnesium, calcium, iron, zinc, manganese), antioxidant activity, total phenolic and total flavonoid content of common bean significantly decreased at the end of 12 months storage compared with before storage, while the contents of heavy metals such as Co, Sn and Pb increased after storage. In addition to, highly significant and positive correlations were determined between L* and WI, b* and C*, Dg and Da, Dg and Sa, Sa and Sv, P and K, P and Ca, ash and pH, Zn and Cu, Se and As. The results of this study clearly indicated that low seed moisture content was the most suitable to maintain the quality of common beans for long-term storage.     

Effect of heat treatment on quality, thermal and pasting properties of sweet potato starch during yearlong storage

BACKGROUND: Proper postharvest handling and storage of sweet potato is an important link in the chain from producer to consumer or manufacturing industry. Heat treatments have been used as a non‐chemical means to modify the postharvest quality and reduce pathogen levels and disease development of a wide variety of horticultural products. The objective of this study was to investigate the effects of hot water treatment (HWT) on the quality, gelatinisation enthalpy and pasting properties of sweet potato starch during long‐term storage. The weight loss, sprouting, spoilage and sugar content of sweet potato were also determined. RESULTS: HWT significantly inhibited the sprouting and decay of sweet potato during the storage period. There were no significant differences (P < 0.05) in the pasting properties and onset (T_O), peak (T_P) and endset (T_E) temperatures of gelatinisation of sweet potato starch among all treatments, especially between heat‐treated and non‐heat‐treated samples. HWT also had no significant impact on the quality of the internal components of the roots. Less than 4% of the yearlong‐stored roots were discarded owing to spoilage. HWT supplied a lethal dose of heat to surface pathogens and black spot without damaging the nutritional and processing qualities of sweet potato. CONCLUSION: HWT was an effective method to reduce root sprouting and deterioration without significant impact on the quality of the internal components of sweet potato. This novel technique will open a new avenue to extend the storage life of sweet potato with good quality and minimal waste. Copyright © 2011 Society of Chemical Industry     

灵芝酸奶的研制

以灵芝深层发酵滤液和脱脂乳为主要原料,制备灵芝保健酸奶,研究灵芝酸奶的生产工艺和贮藏过程中的风味物质及菌相变化。结果表明,嗜热链球菌(S.t)与保加利亚乳杆菌(L.b)的接种比例为1︰1,接种量为3%,灵芝发酵滤液添加量为20%,同时添加6%的蔗糖,42℃下发酵4 h,得到质量较好的灵芝酸奶。与对照酸奶(未加灵芝发酵液)相比,灵芝酸奶中的乳酸菌含量显著提高,L.b/S.t比值增加;在贮藏过程中,灵芝酸奶的黏度、乙醛和丁二酮的质量浓度都呈现出先升后降的趋势,并且黏度和乙醛质量浓度均高于对照酸奶,多糖质量浓度显著高于对照酸奶,灵芝酸奶有较高的营养保健价值。     

Conformational and thermal properties of phaseolin,the major storage protein of red kidney bean (Phaseolus vulgaris L.)

BACKGROUND: A previous study of various functional and physicochemical properties of phaseolin indicated good potential of phaseolin for application in food formulations in view of its excellent functional properties. The aim of the present study was to explore the conformational and thermal properties of phaseolin in the presence of protein structural perturbants by intrinsic fluorescence emission spectroscopy and differential scanning calorimetry. Raman spectroscopy was also used to characterise the secondary structures of phaseolin. RESULTS: The Raman spectrum of phaseolin indicated that β‐sheets and random coils were the major secondary structures. Intrinsic fluorescence emission spectroscopy confirmed the structural peculiarity and compactness of phaseolin, as evidenced by the absence of any shift in emission maximum (λ_max) in the presence of structural perturbants such as sodium dodecyl sulfate (SDS), guanidine hydrochloride, urea and dithiothreitol (DTT). Increasing NaCl concentration enhanced the thermal stability of phaseolin. Addition of chaotropic salts (1 mol L^?1) caused progressive decreases in thermal stability following the lyotropic series of anions. Decreases in thermal denaturation temperature (T_d) and enthalpy change (ΔH) were observed in the presence of protein perturbants such as SDS, urea and ethylene glycol, indicating partial denaturation and a decrease in thermal stability. DTT and N‐ethylmaleimide had little effect on the thermal properties of phaseolin, confirming that phaseolin, a 7S globulin, is devoid of inter‐polypeptide disulfide bonds. CONCLUSION: The data presented here demonstrate the contributions of hydrophobic and electrostatic interactions and hydrogen bonding to the conformational stability of phaseolin. Copyright © 2010 Society of Chemical Industry     

Biochemical,textural and microstructural changes in whole‐soya bean cotyledon sufu during fermentation

This study aims to investigate the nutritional value of sufu and reduce environmental problems caused by okara, which results from the traditional processing method of sufu. The feasibility of the whole‐soya bean cotyledon sufu (WSCS) processing method, which does not produce okara, was investigated. WSCS was prepared by ripening okara‐containing tofu through various hydrolytic enzymes secreted by Actinomucor elegans for 70 days. After fermentation, total nitrogen, amino nitrogen and lipid contents were found to be lower in WSCS than in traditional sufu (TS), whereas contents of reducing sugar, dietary fibre, isoflavone aglycone and soya bean polysaccharide were higher in WSCS than in TS. The hardness, springiness and adhesiveness of WSCS were 249.703 ± 0.500 g, 0.606 ± 0.008 and 8.393 ± 0.032 J, respectively. The corresponding values for TS were 264.863 ± 0.572 g, 0.615 ± 0.007 and 7.516 ± 0.031 J, respectively. In addition, microstructural changes in WSCS and TS during fermentation were observed through scanning electron microscopy. The results from this study may provide a basis for industrial production of WSCS.     

Quality changes in the fresh water prawn, Macrobrachium rosenbergii during storage on ice

The effect of stratification in ice on the quality of fresh water prawns was monitored by microbiological, subjective and objective textural analyses. In general, prawns in the lower layers of ice exhibited more marked textural changes and greater numbers of potential spoilage bacteria were found on them. No connection was found between the number of proteolytic bacteria and textural changes in the prawn muscle.     

Chemical and nutritive changes in herring meal during storage at different temperatures with and without antioxidant treatment

Herring meals prepared with and without the addition of 0.025% of 1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline (EQ) were stored for ten months at -20 ºC and 21 ºC. Storage changes in the biologically determined energy and protein values of the meals were monitored and related to changes in the chemical characteristics of the meal. Antioxidant treatment stabilised the meal lipid against oxidative changes resulting in loss of solubility, decline in iodine value and formation of peroxides and malonaldehyde. The effect of storage temperature on the course of oxidation depended upon whether the meal was treated with EQ. Lipid in meals without EQ tended to show greater change early in the storage period at -20 ºC. Antioxidant-treated meals showed protection of the protein against changes leading to reduced digestibility and lysine availability. Either antioxidant treatment or storage at -20 ºC protected the biological availability of the energy-supplying nutrients present in the meal.     

Spoilage changes in the deep water fish, smooth oreo dory during storage in ice

Smooth oreo dory ( Pseudocyttus maculatus ), a deep water fish, was monitored for changes during storage in ice. Based on the sensory evaluation of the cooked flesh the storage life was 8 days for acceptable quality fish.
Bacterial counts of flesh and surface, the loss of inosine monophosphate (IMP) and the K value showed significant changes during the storage life. Therefore these were found to be useful for monitoring loss of freshness and development of spoilage. After 13 days there were off flavours in the cooked fish, dephosphorylation of IMP had levelled off, and the K value had reached 70%.
The changes that occurred during storage of this deep water species in ice were similar to those changes commonly observed in demersal species from shallow temperate coastal waters.     

热水处理后环境放置期间黄瓜果实温度及抗氧化系统变化

为探讨热水处理后黄瓜果实在非低温贮藏环境放置期间果体温度及抗氧化系统的变化,该试验将热水处理(40℃、20 min)后的黄瓜果实在非低温贮藏环境[20℃,相对湿度(55±5)％]中放置不同时间(0、1、2、4、8 h),并同时测定其果体温度和抗氧化系统的变化.结果表明:热水处理后0 h黄瓜果体温度高达36.5℃,随后的...     

Drip loss,peroxidase and sensory changes in kiwi fruit slices during frozen storage

The biochemical, sensory and drip loss changes that occur during processing and prolonged frozen storage of kiwi fruit slices (cvs Abbott and Hayward) were studied. Fruit slices were frozen at ?40°C, packed in polyethylene bags and stored at ?18°C for 11 months. Maturity characteristics (pH, acidity, dry matter, soluble solids) were determined on raw fruit. Objective (proteins, peroxidase (EC 1.11.1.7) activity, drip loss) and subjective (sensory tests) analyses were carried out during processing and storage, and indicated a good quality of the frozen kiwi fruit slices after 11 months of storage. There were significant differences (P < 0.05) between the studied varieties with respect to drip loss during frozen storage and colour after 11 months. Best results were obtained with cv Hayward. This variety showed less drip loss after thawing and after 11 months storage presented the same green colour as after freezing, while cv Abbott became yellowish-green.     

Concentrations of biogenic amines in fish,squid and octopus and their changes during storage

The concentrations of seven biogenic amines (BA) were simultaneously determined in 74 samples of fish, squid and octopus, by the method of HPLC coupled with pre-column derivatisation. The relationship between the formation of BA in aquatic products and the growth of microbial flora during storage was also investigated. Results showed that putrescine, cadaverine, histamine and tyramine were the dominant BA in the studied samples, but the concentrations of histamine and tyramine were mostly less than 50 and 100 mg kg⁻¹, respectively. Freezing can effectively prevent the formation of BA, but the levels of putrescine, cadaverine, histamine and tyramine significantly increased (p < 0.05) during storage at 4 and 25 °C. The growth of mesophilic or psychrophilic bacteria in blue scad and octopus strongly and positively correlated with the formation of amines (such as putrescine, cadaverine, histamine and tyramine) during storage, except for histamine in octopus.     

Decline in antioxidant capacity of Indian herbal teas during storage and its relation to phenolic content

The changes in the stability of antioxidant capacity with time and its relation to the phenolic content were evaluated in eight Indian herbal teas. These herbal teas are claimed to be antistress, immunomodulator, anti-aging, anti-inflammatory, appetizer, stimulant, blood purifier, energizer, antidepressant, antidiabetic, rejuvenative, analgesic, antiviral, nervine, diuretic, antihypertensive and memory enhancer. Antioxidant capacity was determined over a period of 15 months from the date of their procurement using assays for SOD mimetic activity, LPO inhibitory capacity and total thiol content, which decreased positively with time. Total phenolic content was determined spectrometrically according to the Folin-Ciocalteu method and calculated as gallic acid equivalents (GAE). Herbal teas with higher phenolic content showed a comparatively less decline in antioxidant capacity. The SOD mimetic activity values in control samples (at the time of procurement) were seen to be in the range of 54.63–93.64 units/min/mg of extract which after 15 months of storage decreased upto 7.4-folds in some samples. LPO inhibitory capacity was observed upto 96.75% in herbal tea E at the time of procurement which dropped to 63.85% inhibition of MDA formation/5μl of extract after 15 months. In case of total thiol, the values were seen in the range of 0.55–1.71 mg/g and after 15 months it was from 0.12 to 0.21 mg/g. In all these cases high antioxidant activity was seen in the samples with higher phenolic content which also showed comparatively less decline in antioxidant capacity after considerable storage time. The results have significance, as most of the herbal teas available in the local markets in India do not carry any information regarding the period of use without decline in its beneficial effects.     

Stability of anthocyanins in frozen and freeze-dried raspberries during long-term storage: in relation to glass transition

Abstract: Anthocyanins, natural plant pigments in the flavonoid group, are responsible for the red color and some of the nutraceutical benefits of raspberries. This study explores anthocyanin degradation in frozen and freeze‐dried raspberries during storage in relation to glass transition temperatures. Frozen raspberries were stored at ?80, ?35, and ?20 °C, while freeze‐dried raspberries were stored at selected water activity (a_w) values ranging from 0.05 to 0.75 at room temperature (23 °C) for more than a year. The characteristic glass transition temperatures (T′_g) of raspberries with high water content and glass transition temperature (T_g) of raspberries with small water content were determined using a differential scanning calorimeter. The pH differential method was used to determine the quantity of anthocyanins in frozen and freeze‐dried raspberries at selected time intervals. The total anthocyanins in raspberries fluctuated during 378 d of storage at ?20 and ?35, and ?80 °C. Anthocyanin degradation in freeze‐dried raspberries ranged from 27% to 32% and 78% to 89% at a_w values of 0.05 to 0.07 and 0.11 to 0.43, respectively, after 1 y. Anthocyanins were not detectable in freeze‐dried raspberries stored at a_w values of 0.53 to 0.75 after 270 d. First order and Weibull equations were used to fit the anthocyanin degradation in freeze‐dried raspberries. The 1^st‐order rate constant (k) of anthocyanin degradation ranged from 0.003 to 0.023 days^?1 at the selected water activities. Significant anthocyanin degradation occurred in both the glassy and rubbery states of freeze‐dried raspberries during long‐term storage. However, the rate of anthocyanin degradation in freeze‐dried raspberries stored in the glassy state was significantly smaller than the rate of anthocyanin degradation in the rubbery state.