Effects of hot-water and steam blanching of sliced potato on polyphenol oxidase activity

The worldwide potato production is considered the fourth-most important food sector due to the increasing use of potatoes as raw materials for high-convenience food. Enzymatic browning, due to polyphenol oxidase (PPO), is related to unacceptability by consumer. Among antibrowning agents, thermal treatments are viable alternatives. In this study, the efficacy of hot-water and steam blanching at 80–90 °C of potato slices (1-cm thick) was evaluated in terms of colour changes as well as PPO inactivation kinetics, substrate specificity and transition state parameters. In general, all treatments [1] bleached the slices, [2] inactivated PPO and [3] reduced its kinetic efficiency. Results from thermal inactivation kinetics promoted hot-water blanching at 90 °C for approx. 2 min as the fastest treatment to obtain enzymatic-stable potato slices. Moreover, steam blanching required more energy (53.93 ± 1.24 kJ mol⁻¹) than hot-water treatment (41.41 ± 4.51 kJ mol⁻¹) to reach the transition state and then to unfold the PPO enzyme.     

中式烹饪对马铃薯中抗性淀粉及主要营养物质的影响

研究了不同烹饪方式对马铃薯中的抗性淀粉及主要营养物质含量的影响,为科学评价居民膳食营养状况与选择合理的烹饪方法提供理论依据。将马铃薯清洗、去皮、切割,以炒、烧、炸、蒸、焯的方式进行烹饪,采用AkerbergAKE法测定烹饪前后马铃薯中抗性淀粉的含量变化、计算保留因子,采用国标方法分析烹饪前后马铃薯中总淀粉、蛋白质、脂肪、水分的含量变化。马铃薯经烹饪处理后,抗性淀粉含量均显著下降,其中经炒、烧处理后,抗性淀粉保留因子较高,分别为34%、30%,而经炸、蒸、焯处理后保留因子较低,其中焯制后保留因子最低,为24%;不同烹饪处理后,马铃薯的总淀粉、蛋白质含量均表现出不同程度的下降,水分、脂肪含量并没有表现出一致的下降趋势。结果表明,马铃薯经不同烹饪处理后,抗性淀粉、总淀粉、蛋白质、脂肪、水分等含量均发生变化,并且经不同烹饪方法处理后,含量变化又有很大的差异。      

Effect of temperature on lipid‐derived volatile compounds in boiled potato during storage

BACKGROUND: The aroma of boiled potatoes is greatly appreciated by consumers. Although it is formed by 150 volatile compounds, only a few seem to actually contribute to the characteristic aroma. In addition, potatoes have to be stored at a low temperature after harvest to guarantee a year‐round supply. However, even at low temperatures, tuber volatile composition is modified during storage. The aim of the present study was to investigate the effect of storage temperature on boiled potato volatile constituents, mainly focused on lipid‐derived components, by considering different varieties stored at 4 °C and 8 °C. RESULTS: It was found that fewer lipid‐derived components were obtained when the potato tubers were stored at 4 °C rather than 8 °C. Specifically, the amounts of 2,4‐decadienal isomers and hexanal increased with the storage time, particularly at 8 °C. Similarly, pentanal and nonanal, which are autoxidation products, occurred to a greater extent at higher temperatures. In contrast, the levels of sugar‐derived compounds, in general, increased during storage at 4 °C rather than 8 °C as a result of higher content of sugars at low temperature. CONCLUSION: The effect of storage temperature on lipid‐derived volatile components in boiled potato appears to depend on the variety studied. Generally speaking, lower temperatures during storage promote sugar content and, as a consequence, sugar‐derived products. At the same time, lower temperatures result in less lipid oxidation and, therefore, a fewer lipid‐derived compounds. Copyright © 2009 Society of Chemical Industry     

Glycoalkaloids in potato tubers: the effect of variety and drought stress on the α‐solanine and α‐chaconine contents of potatoes

Six varieties of Solanum tuberosum L potato grown in the Bolivian highlands under drought stress, with and without irrigation, were analysed for their content of glycoalkaloids (GAs). The plant material consisted of three drought‐tolerant varieties from a local breeding programme (PROINPA), Potosina, Chapaquita and Pampeña, and three control cultivated varieties, Malcacho, Sani Imilla and Desiree, either susceptible or relatively tolerant to drought. α‐Solanine and α‐chaconine were quantified in both the peel and flesh of the tubers. A significant increase in GA concentration (α‐solanine + α‐chaconine) was observed under drought stress conditions in most varieties; average concentration increases of 43 and 50% were registered in the improved and control cultivars respectively. In all tested cultivars, however, the GA concentration remained lower than the recommended food safety level (200 mg kg⁻¹ fresh tubers). It ranged from 52.4 to 100 mg kg⁻¹ fresh tubers in the improved cultivars and from 55.6 to 122.3 mg kg⁻¹ fresh tubers in the controls. In the improved and control varieties the α‐solanine content averaged 42.6 and 35.4% of the total potato GAs respectively and was not significantly affected by drought stress, except in Desiree. In all conditions the peel contained the greatest proportion of total GAs. The hybrid variety Pampeña (new drought‐tolerant variety) contained the lowest amounts of GAs, which were lower than those of the control varieties, with and without irrigation. © 2000 Society of Chemical Industry     

Variation in glycoalkaloid concentration of potato tubers harvested from mature plants

Individual tubers from mature plants of cultivars Pentland Dell and Estima were harvested from experimental plots in two successive years and analysed for α‐solanine, α‐chaconine and total glycoalkaloid concentration (α‐solanine and α‐chaconine combined) using high‐performance liquid chromatography. Mean tuber glycoalkaloid concentration per plant was strongly affected by genotype and was much higher in plants of Pentland Dell (10.0 and 16.3 mg per 100 g fresh weight in 1994 and 1995, respectively) than Estima (4.0 and 4.3 mg per 100 g fresh weight in 1994 and 1995, respectively). The variation between plants in mean tuber glycoalkaloid concentration, expressed as coefficient of variation, was similar for the two cultivars in both years. Variation within plants was higher for cultivar Pentland Dell than Estima for both years but it was statistically significant only in 1995. Tuber position within a plant had no effect on glycoalkaloid concentrations in tubers of similar size. An inverse relationship between total glycoalkaloid concentration and tuber fresh weight of individual tubers was found for both cultivars and small tubers of Pentland Dell (20–40 g fresh weight) exceeded the safety limit of 20 mg per 100 g fresh weight. The pattern of glycoalkaloid accumulation differed between genotypes and appeared related to tuber growth. The implications of these results in terms of food safety are discussed. © 1999 Society of Chemical Industry     

Changes in selected physical property and enzyme activity of rice and barley koji during fermentation and storage

Koji are solid-state fermentation products made by inoculating steamed grains with the spores of fungi, particularly Aspergillus spp. This research was undertaken to identify the fermentation and storage conditions optimal for the production and maintenance of selected hydrolytic enzymes, such as α-amlyase and protease, in koji. Steamed rice and barley were inoculated with 2 × 10 (11) Aspergillus oryzae spores per kilogram of grains and fermented for 118 h in a growth chamber at 28 to 32 °C with controlled relative humidities. Samples were drawn periodically during fermentation and storage at -20, 4, or 32 °C, and α-amylase and protease activity, mold counts, a(w), moisture contents, and pH of collected samples were determined. It was observed that the a(w), moisture contents, and pH of the koji were influenced by the duration of fermentation and temperature of storage. The α-amylase activity of both koji increased as the populations of A. oryzae increased during the exponential growth phase. The enzyme activity of barley koji was significantly higher than that of rice koji, reaching a peak activity of 211.87 or 116.57 U at 46 and 58 h, respectively, into the fermentation process. The enzyme activity in both products started to decrease once the mold culture entered the stationary growth phase. The protease activities of both koji were low and remained relatively stable during fermentation and storage. These results suggest that rice and barley koji can be used as sources of α-amylase and desired enzyme activity can be achieved by controlling the fermentation and storage conditions. PRACTICAL APPLICATION: Amylases and proteases are 2 important hydrolytic enzymes. In the food industry, these enzymes are used to break down starches and proteins while reducing the viscosity of foods. Although amylases and proteases are found in plants and animals, commercial enzymes are often produced using bacteria or molds through solid state fermentation, which is designed to use natural microbial process to produce enzymes in a controlled environment. A properly produced and maintained koji with a high hydrolytic enzyme activity can serve as an important source of the enzymes for the food industry.     

藤稔葡萄不同节位芽的发育及结果能力分析

花芽分化是葡萄产量形成的生理基础。为了解葡萄不同节位芽发育的情况,本试验以6年生藤稔品种为试材,通过在枝条不同节位进行修剪并仅保留顶部2个芽的处理,研究了不同节位芽萌发新梢的开花及结果习性。结果表明,不同节位的修剪处理均不同程度地增加了结果枝的粗度和花序数,果穗和果实性状也有所提高。     

壳聚糖协同次氯酸盐对北碚447锦橙贮藏品质的影响

为探讨壳聚糖协同次氯酸盐对北碚447锦橙贮藏品质的影响,用壳聚糖、壳聚糖协同次氯酸钠、壳聚糖协 同次氯酸钙涂膜处理北碚447锦橙,每5 d测定1 次果实贮藏期间果肉中可溶性固形物、总糖、总酸质量分数和VC、 总黄酮、总酚含量等品质指标。结果表明：壳聚糖具有良好的果品品质保持作用,能较好地保持果实VC、总酚含 量以及总糖质量分数;同时,壳聚糖与次氯酸盐协同涂膜对北碚447锦橙品质保持作用明显优于单独使用壳聚糖, 其中0.01 g/mL壳聚糖＋200 mg/L Ca(ClO)2处理效果最显著,有效地延缓了贮藏期间果实品质的下降。说明壳聚糖协 同次氯酸钙能够有效提高北碚447锦橙的贮藏品质和延长其贮藏期。     

Cloning, sequencing and characterization of the alpha-aminoadipate reductase gene (LYS2) from Saccharomycopsis fibuligera

The gene putatively encoding alpha-aminoadipate reductase (AAR) was isolated successfully by degenerate PCR and chromosome walking, based on cassette PCR methods, from the dimorphous yeast Saccharomycopsis fibuligera PD70 and was named SfLYS2. Sequence analysis revealed that it contained a putative open reading frame (ORF) of 4161 bp and encoded a polypeptide of 1386 amino acids. The deduced translation product shared an identity of 53% and 51% to the Lys2p homologues of Candida albicans and Saccharomyces cerevisiae, respectively. An atypical TATA box and a GCN4-box element were found in the 5'-upstream region. Genomic Southern hybridization suggested the presence of a single locus of SfLYS2 in the S. fibuligera genome. Expression of the ORF of SfLYS2 in a lys2(-) strain of S. cerevisiae could functionally complement the lysine mutant of the S. cerevisiae strain. S. fibuligera could use lysine as the sole nitrogen source but its growth was inhibited on the alpha-aminoadipate (AA) medium. Approximately 90% of the mutants of S. cerevisiae resistant to AA are lysine auxotrophs; in contrast all the mutants of S. fibuligera resistant to AA recovered in this work were not lysine auxotrophs.     

蒸煮工艺对鲣鱼鱼柳品质的影响

以鲣鱼为原料,考察了两种不同的蒸煮工艺(T1、T2)对蒸煮过程中鱼柳的升温曲线、失水率、失重率、色泽、质构和组胺含量等的变化情况,分析两种蒸煮工艺对鱼柳蒸煮品质影响的差异,找出两种工艺的优缺点。结果表明,蒸煮工艺T1蒸煮损失较低,鱼柳得率比T2高1%~2%,蒸煮时间比T2短6~8 min,蒸煮过程中鱼肉色泽变化稳定,蒸煮完成后具有较好的质构特性,并且T1能有效降低鲣鱼肉中的盐含量。蒸煮工艺T2步骤相对简单,总加工时间比T1短20~30 min,组胺产生量比(T1)少约18 mg/kg,同时所得鱼柳还具有较高的非蛋白氮,气味较浓郁。两种蒸煮工艺各有优势,企业可以根据鲣鱼新鲜度及生产条件选择合适生产工艺。      

Cloning and characterization of a second alpha-amylase gene (LKA2) from Lipomyces kononenkoae IGC4052B and its expression in Saccharomyces cerevisiae

Lipomyces kononenkoae secretes a battery of highly effective amylases (i.e. alpha-amylase, glucoamylase, isoamylase and cyclomaltodextrin glucanotransferase activities) and is therefore considered as one of the most efficient raw starch-degrading yeasts known. Previously, we have cloned and characterized genomic and cDNA copies of the LKA1 alpha-amylase gene from L. kononenkoae IGC4052B (CBS5608T) and expressed them in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Here we report on the cloning and characterization of the genomic and cDNA copies of a second alpha-amylase gene (LKA2) from the same strain of L. kononenkoae. LKA2 was cloned initially as a 1663 bp cDNA harbouring an open reading frame (ORF) of 1496 nucleotides. Sequence analysis of LKA2 revealed that this ORF encodes a protein (Lka2p) of 499 amino acids, with a predicted molecular weight of 55,307 Da. The LKA2-encoded alpha-amylase showed significant homology to several bacterial cyclomaltodextrin glucanotransferases and also to the alpha-amylases of Aspergillus nidulans, Debaryomyces occidentalis, Saccharomycopsis fibuligera and Sz. pombe. When LKA2 was expressed under the control of the phosphoglycerate kinase gene promoter (PGK1(p)) in S. cerevisiae, it was found that the genomic copy contained a 55 bp intron that impaired the production of biologically active Lka2p in the heterologous host. In contrast to the genomic copy, the expression of the cDNA construct of PGK1p-LKA2 in S. cerevisiae resulted in the production of biologically active alpha-amylase. The LKA2-encoded alpha-amylase produced by S. cerevisiae exhibited a high specificity towards substrates containing alpha-1,4 glucosidic linkages. The optimum pH of Lka2p was found to be 3.5 and the optimum temperature was 60 degrees C. Besides LKA1, LKA2 is only the second L. kononenkoae gene ever cloned and expressed in S. cerevisiae. The cloning, characterization and co-expression of these two genes encoding these highly efficient alpha-amylases form an important part of an extensive research programme aimed at the development of amylolytic strains of S. cerevisiae for the efficient bioconversion of starch into commercially important commodities.     

Effect of the Malting Barley Variety (Hordeum vulgare L) on Fermentability1

The influence of the malting barley genotype on the apparent attenuation limit (AAL) was investigated. The AAL level correlated closely with the maltose concentration in the wort but was not affected by other fermentable sugars or by the total carbohydrate content. The chemical composition, modification, amylolytic enzyme activities and several starch properties of selected malts were studied in detail. Variations in the maltose concentration could almost solely be traced back to genotype‐dependent disparities of β‐amylase thermostability. These differences are due to interallelic polymorphisms of the β‐amylase gene and are easily detected by PCR. Hence, PCR primers offer remarkable prospects for breeding barley on the basis of a marker‐assisted selection (MAS).     

不同品种甘薯香味组分差异性分析

为了比较不同干燥方式对甘薯固体香料的影响,本研究以新鲜的甘薯为研究对象,烘烤后进行红外干燥、冷冻干燥、微波真空干燥和真空干燥,用气相色谱-质谱法（Gas Chromatography-Mass Spectrometry,GC-MS）分析检测甘薯固体香料的挥发性/半挥发性成分,并进行主成分分析探究不同干燥方法对挥发性/半挥发性成分的影响,用扫描电子显微镜探究不同的干燥方式对其表面结构的影响。结果表明：干燥后甘薯固体香料挥发性/半挥发性物质含量从高到低依次为真空干燥、微波真空干燥、红外干燥、冷冻干燥,含量最高为128.87 μg/g,主要香味物质有对甲氧基肉桂酸辛酯、棕榈油酸、香叶基芳樟醇、5-羟甲基糠醛、（9Z）-十八碳-9,17-二烯醛。真空干燥固体香料表面结构相较于其他三种干燥方式,真空干燥的表面有较多的水分蒸发通道及孔洞,且结构密度适中,对固体香料的吸附能力及挥发香味有积极影响。综上所述,真空干燥适用于甘薯固体香料的干燥制备,为甘薯固体香料的开发应用奠定了理论基础。     

魔芋葡甘露聚糖-壳聚糖复合涂膜对北碚447锦橙贮藏品质的影响

为探究魔芋葡甘露聚糖-壳聚糖复合涂膜对北碚447锦橙贮藏品质的影响,分别采用0.5%魔芋葡甘露聚糖+1%壳聚糖复合涂膜,0.5%魔芋葡甘露聚糖涂膜和空白处理北碚447锦橙。以5 d为一个周期,15 ℃温度贮藏,共贮藏5个周期,测定贮藏期间果实的总糖、可滴定酸、V_C、固形物、总酚等指标。结果表明,复合涂膜处理可有效延缓果实品质的下降,与0.5%魔芋葡甘露聚糖涂膜和空白处理对比,复合膜组能够明显抑制果实总糖、可滴定酸、V_C、总黄酮、总酚含量的下降,减缓果实中丙二醛的积累,使锦橙保持了较好的果实品质。证明了复合涂膜处理相比单独0.5%KGM保鲜效果更好。     

Dehydroepiandrosterone (DHEA) metabolism in Saccharomyces cerevisiae expressing mammalian steroid hydroxylase CYP7B: Ayr1p and Fox2p display 17beta-hydroxysteroid dehydrogenase activity

We have engineered recombinant yeast to perform stereospecific hydroxylation of dehydroepiandrosterone (DHEA). This mammalian pro-hormone promotes brain and immune function; hydroxylation at the 7alpha position by P450 CYP7B is the major pathway of metabolic activation. We have sought to activate DHEA via yeast expression of rat CYP7B enzyme. Saccharomyces cerevisiae was found to metabolize DHEA by 3beta-acetylation; this was abolished by mutation at atf2. DHEA was also toxic, blocking tryptophan (trp) uptake: prototrophic strains were DHEA-resistant. In TRP(+) atf2 strains DHEA was then converted to androstene-3beta,17beta-diol (A/enediol) by an endogenous 17beta-hydroxysteroid dehydrogenase (17betaHSD). Seven yeast polypeptides similar to human 17betaHSDs were identified: when expressed in yeast, only AYR1 (1-acyl dihydroxyacetone phosphate reductase) increased A/enediol accumulation, while the hydroxyacyl-CoA dehydrogenase Fox2p, highly homologous to human 17betaHSD4, oxidized A/enediol to DHEA. The presence of endogenous yeast enzymes metabolizing steroids may relate to fungal pathogenesis. Disruption of AYR1 eliminated reductive 17betaHSD activity, and expression of CYP7B on the combination background (atf2, ayr1, TRP(+)) permitted efficient (>98%) bioconversion of DHEA to 7alpha-hydroxyDHEA, a product of potential medical utility.     

Effect of soaking,cooking and crude α-galactosidase treatment on the oligosaccharide content of cowpea flours

Abstract : The effects of soaking, cooking and crude α-galactosidase treatment on the level of stachyose and raffinose present in cowpea flours were investigated. Soaking for 16 h resulted in an average reduction of 26·2% for stachyose and 28·0% for raffinose, while cooking for 50 min resulted in a reduction of 28·6% for stachyose and 44·0% for raffinose. On the other hand, treatment of cowpea flours for 2 h at 50°C with crude fungal preparations having an α-galactosidase activity equivalent to 64 units μg^?1 protein, brought about a mean decrease of 82·3% for stachyose and 93·3% for raffinose. These results show that the enzyme treatment was more effective in removing the raffinose-family oligosaccharides and hence could be a useful technique for control of the flatulence-inducing activity of cowpea flours.     

Effect of cold shock on the enhancement of β‐amylase activity during malting and malt processability for a red sorghum intended for brewing use

The low β‐amylase activity of sorghum malt is a major concern when malts are intended for use in brewing. Several studies have shown that the germination temperature plays an important role in β‐amylase synthesis. In this study, the cold shock treatment was envisioned as a means of improving β‐amylase synthesis during red sorghum malting. The results show that, when a high‐frequency decrease in the germination temperature is used, the obtained malt exhibits a significantly increased β‐amylase activity. This study shows that this increase is not sufficient to consider cold shock as a means of improving β‐amylase activity for red sorghum brewing use, as the processabilty of the malts is unsatisfactory. Copyright © 2015 The Institute of Brewing & Distilling     

Effect of cooking or handling conditions on the furan levels of processed foods

The aim of this study was to investigate the possible effects of cooking or handling conditions on the concentration of furan in processed foods. The analytical method used to analyse furan levels in foods was optimized based on solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). In baby soups, the concentration of furan decreased by up to 22% after opening a lid for 10 min. In the baby food in retort packaging, the level of furan was reduced by 15–33% after heating the foods at 50°C without a lid. Furan in rice seasonings was evaporated completely after heating the foods at 60°C. Regarding powered milk, the levels of furan were too low to be compared under various conditions. The levels of furan decreased to 58% in beverage products for babies, after storing them at 4°C for 1 day without a lid. The levels of furan in canned foods such as cereal and vegetable were reduced by zero to 52% when they were stored without stirring in a refrigerator at 4°C for 1 day. When we boiled canned fish, the furan present was almost completely evaporated. It is recommended that canned meats be heated up to 50–70°C for the reduction (26–46%) of furan levels. The levels of furan in instant and brewed coffee samples were significantly reduced after storing for 11 to 20 min at room temperature without a lid (p < 0.05).