Changes in physicochemical and sensory-properties of irradiated rice during storage

Milled aromatic rice (KDML-105) was γ-irradiated at doses of 0, 0.2, 0.5 and 1.0 kGy. Changes in physicochemical and sensory properties were recorded during subsequent storage in polyethylene bags at ambient temperature for 1 year. Similar trends were observed in both irradiated and non-irradiated samples. Insignificant changes in yellowness and total solids in cooking water were observed during storage of irradiated rice compared with those of naturally-aged rice. Irradiated rice showed less increase in Rapid Visco Analyzer (RVA) setback, greater reduction of RVA breakdown, and softer texture than non-irradiated rice. It also had a softer but slimy texture, off odour and inferior taste compared with the non-irradiated sample. Based on overall acceptability to panelists preferring fresh rice, non-irradiated rice could be stored for more than 1 year while rice irradiated at 0.2, 0.5 and 1.0 kGy had shelf lives of 9, 7 and 2 months, respectively.     

Evaluation of physicochemical properties of plasma treated brown rice

A novel processing technology is developed to modify brown rice in a more selective way with the help of low-pressure plasma. The microstructure of the brown rice surface and the cooking, textural and iodine-staining properties of plasma treated brown rice are determined. The plasma treatment results in an etching of brown rice surface, which allows water to be easily absorbed by the rice kernel during soaking. After plasma treatment, the cooking time of brown rice is reduced, and the cooked brown rice has a soft texture and is easier to chew. In addition, the increment of the iodine-stained area indicates that the kernel structure of brown rice is substantially affected by plasma. Thus, plasma treatment can be used to improve the cooking properties and the quality of brown rice.     

Changes in physicochemical properties and bactericidal efficiency of acidic electrolyzed water ice and available chlorine decay kinetics during storage

Acidic electrolyzed water ice (AEW ice) is a new kind of bactericide used in preservation or cold sterilization of food products. The aim of this study was to investigate changes in the physicochemical properties (oxidation reduction potential (ORP), pH value and available chlorine concentration (ACC)), bactericidal efficiency, and decay kinetics of available chlorine in AEW ice during 10 h of storage time. Results indicated that pH changes of AEW ice did not have a significant difference (p > 0.05) during the first 6-h storage, after 6 h, the pH of AEW ice prepared with ≤1 g/l NaCl solution changed more slowly than that of AEW ice prepared with >1 g/l NaCl solution. Both ORP and ACC decreased with storage time. The ACC of AEW ices prepared from >1.5 g/l NaCl solutions decreased faster and in a greater extent than those prepared from ≤1.5 g/l NaCl solutions. According to the correlation analysis, the correlation coefficients between pH, ORP, and ACC and Vibrio parahaemolyticus inactivation were −0.831, 0.787 and 0.944, respectively, and those between the above parameters and Listeria monocytogenes inactivation were −0.814, 0.701 and 0.97, respectively. Based on the kinetic study, the decay of ACC fitted the first order kinetics.     

Effects of the addition of hemp powder on the physicochemical properties and energy bar qualities of extruded rice

Extruded rice/hemp mixtures were prepared by mixing defatted and whole hemp powders with rice flour at varying hemp levels (0%, 20%, 30% and 40%). The influence of hemp powder type and level on physicochemical and antioxidant properties was studied. The bulk densities of the extruded rice/hemp samples increased with increase in levels of added hemp powder. The extrudates blended with hemp powder had a lower water absorption index than the control (extruded rice without hemp). The extruded rice/whole hemp had more total phenolics and flavonoids and had a better scavenging effect on DPPH radicals than extruded rice/defatted hemp. The highest potential to inhibit β-carotene oxidation was found in extruded rice/40% whole hemp. Increasing amounts of hemp powder resulted in lower equilibrium moisture content of energy bars. The energy bar made with extruded rice/20% whole hemp was preferred for colour, taste and overall acceptability.     

Influence of guar gum addition on physicochemical,microbial, rheological and sensory properties of stirred yoghurt

This study investigated the effects of adding guar gum (0, 0.6 and 0.8 g/100 mL) on the physicochemical, microbial, rheological and sensory properties of stirred yoghurt. Incorporation of guar gum into the yoghurt significantly affected the pH and colour, but did not significantly influence the lactic acid bacteria counts. The magnitudes of apparent viscosity (η_a,100), consistency index (K), yield stress (σ_oc), storage modulus (G′) and loss modulus (G″) for yoghurt samples containing guar gum (0.6–0.8 g/100 mL) were significantly greater than those for the control (without guar gum), indicating that guar gum can improve the steady and dynamic shear rheological properties of yoghurt.     

Effects of superfine grinding on physicochemical and antioxidant properties of Lycium barbarum polysaccharides

The objective of this study was to investigate the effects of superfine grinding on the physicochemical and antioxidant properties of Lycium barbarum polysaccharides (LBP). Superfine grinding treatment could decrease the average molecular weight (changed from 834.0, 85.2 and 70.6 to 538.5, 71.2 and 2.1, respectively), the spherical particle’s heights (changed from 0.86, 0.59 and 0.51 nm to 0.74, 0.55 and 0.43 nm, respectively) and the spherical particle’s diameter (changed from 98.33, 70.67 and 86.33 nm to 88.67, 47.67 and 51.33 nm, respectively) of LBP. After being superfine grinding treated, the ΔH values of LBP changed from −154.6, −136.5 and −105.0 J/g to −220.8, −97.2 and −46.5 J/g, respectively. The IC₅₀ of LBP from treated materials on DPPH radical (4.96, 1.98 and 2.97 mg/mL) and ABTS radical (2.25, 0.20 and 0.25 mg/mL) were extremely lower than those of LBP from untreated materials. The results suggested that superfine grinding treatment enhanced LBP’s antioxidant activities. Molecular weight and solution behavior were key factors in polymer’s antioxidant activities.     

Changes in physicochemical properties of organic hulled rice during storage under different conditions

Effects of packaging materials, storage temperatures and time on physicochemical properties of organic hulled red fragrant rice cv. Hom Daeng were investigated. The samples were vacuum-packed in oriented polypropylene/aluminium/linear low-density polyethylene or nylon/linear low-density polyethylene pouches and stored at ambient temperature or 15 °C for up to 12 months. Results from differential scanning calorimetry indicated that onset and peak temperature of gelatinisation of the aged rice samples increased after the 6th month while enthalpy of gelatinisation initially increased and then decreased after the 8th month. Measurements from the Rapid Visco Analyzer revealed that peak viscosity and breakdown of the rice pastes increased within the first 2 months, then decreased after the 6th month, whereas setback gradually increased during storage. Swelling power, at 70 and 90 °C, of the aged samples, tended to decrease after the 4th month. Lower storage temperature retarded those changes while packaging materials did not influence the changes. Changes in thermal and pasting properties of the aged samples were reversed after adding 2-mercaptoethanol. Hence, an increase in disulphide linkages of oryzenin during storage could play a crucial role in altering those properties. Sensory evaluation indicated a significant increase in hardness of the cooked rice prepared from the longer-aged samples (p ? 0.05). However, the cooked rice samples, deriving from the samples stored at ambient temperature for up to 12 months, were still acceptable for Thai consumers.     

影响米饭质构特性和感官的关键理化因素分析

选取来自统一产区的24个水稻品种,测定了稻米以及其所加工成米饭的理化特性,分析了稻米理化特性与米饭质构特性间的相关性,建立了质构特性及感官与理化因子间的回归方程,进一步分析影响米饭食味品质的一些关键因素。结果表明,淀粉与多个质构参数呈显著（p<0.05）或极显著（p<0.01）正相关关系;蛋白质与各质构参数相关性不大;水分与米饭的弹性显著相关（r=0.448,p<0.05）;游离氨基酸与粘连性极显著负相关（r=-0.576,p<0.01）,与弹性负相关（r=-0.423,p>0.05）;脂肪与硬度显著负相关（r=-0.420,p<0.05）,与其他质构参数也基本呈负相关;长宽比主要与反映淀粉特性的质构参数显著相关。回归分析表明,脂肪和游离氨基酸含量对米饭食用品质影响较大,当这两者含量低时,米饭质构特性更优良,而当游离氨基酸含量高时,米饭适口性好、感官评分值高。      

The effect of direct acidification on the microbiological,physicochemical and sensory properties of probiotic Minas Frescal cheese

Minas Frescal cheeses produced with the addition of the probiotic culture Bifidobacterium Bb‐12 and without (C1) or with (C2) lactic acid were evaluated in relation to the microbiological, physicochemical and sensory properties. After 28 days of storage, the cheeses without lactic acid showed lower moisture and pH, in addition to higher acidity and syneresis. This behaviour influenced the texture profile of the cheeses, making them harder and chewier. The colour attributes L* and b* diminished during the storage. The majority of the consumers classified the cheeses as having good acceptability and they would buy this type of functional food.     

发芽糙米粉理化性质研究

对发芽粳糙米粉和发芽籼糙米粉基本成分、微观结构、热焓特性及糊化性质(RVA)等进行了研究。结果表明:与糙米粉相比,发芽糙米粉中粗脂肪含量降低,蛋白质含量增加,总淀粉含量降低,粗纤维、灰分等含量变化不明显;随着发芽时间的增长,糙米粉峰值粘度、最低粘度、崩解值、最终粘度和回升值都降低;发芽糙米粉峰值温度、起始温度、终止温度及焓值均比糙米粉低,且籼糙米高于粳糙米。扫描电镜结果显示:发芽后糙米粉颗粒结构变得较疏松,棱角不太明显,发芽籼糙米粉颗粒结构较发芽粳糙米粉颗粒结构更加疏松,淀粉颗粒体积更小。      

大米淀粉结构与特性研究进展

大米淀粉是主要的谷物淀粉之一,具有一些独特的结构及物化特征。本文主要从淀粉颗粒结构、生长环结构、Blocklets小体、层状结构、结晶结构及链结构等多尺度结构层次和凝胶化、糊化、回生及消化等特性方面,对大米淀粉结构和物化特性进行了全面的综述,并阐述了大米淀粉不同层级结构对其特性的影响,同时介绍了大米淀粉的主要制备方法与组成成分及其对大米淀粉特性的影响,以期为大米淀粉的研究与开发提供借鉴。     

两种大米淀粉及其磷酸酯淀粉理化特性的比较研究

对比分析2种大米(籼米和粳米)的全粉、淀粉和取代度均为0.068的磷酸酯淀粉的理化特性.粳米的全粉、淀粉和磷酸酯淀粉的膨胀力分别为7.5,10.7,21.6 g/g,分别高于籼米的全粉、淀粉和磷酸酯淀粉的膨胀力(5.8,8.9,17.4 g/g).2种大米淀粉经磷酸酯化后透光率增高,相应淀粉的透光率次之,全粉的透光率最低,籼米的全粉、淀粉和磷酸酯淀粉的透光率分别低于粳米的全粉、淀粉和磷酸酯淀粉的透光率.经快速黏度分析仪测定的糊化特性结果表明,淀粉或变性淀粉膨胀力高,其峰值黏度和崩解值也高,此外,蛋白质含量和直链淀粉含量也极大的影响了淀粉的糊化特性.使用动态流变仪测定的流变特性表明,在相同的温度下,籼米的全粉、淀粉和变性淀粉的储能模量(G')分别比粳米的全粉、淀粉和变性淀粉的储能模量(G')高,对于相同的大米品种,全粉的储能模量(G')最高,变性淀粉的储能模量(G')最低.     

发芽对糙米理化特性的影响

采用富集γ-氨基丁酸(GABA)的优化糙米发芽工艺条件,研究糙米发芽前后内部结构和理化特性的变化,主要包括膨胀度、透明度、冻融稳定性、凝沉特性、糊化特性及质构特性等。结果表明:糙米发芽后,膨胀度增大,且随温度的升高而提高;透光率比发芽前升高了20%;冻融稳定性提高,凝沉特性得到改善,这说明发芽使糙米不易老化,有助于食品货架期的延长;峰值黏度降低,糊化温度基本不变;糙米发芽后凝胶黏性有所提高,硬度和胶凝性均降低;电镜分析结果显示,发芽后整个米粒结构变得较疏松。通过对糙米淀粉酶活力的测定,表明发芽后糙米淀粉酶活力上升。综上得出,发芽对糙米的理化特性有一定的改善作用。     

Changes in physicochemical and organoleptic properties of traditional Iranian cheese Lighvan during ripening

Lighvan cheese was studied to determine the physicochemical and biochemical changes over 90 days of ripening in brine. Acidity, pH, dry matter, fat values, lipolysis level, water‐soluble nitrogen (WSN), total nitrogen (TN), ripening index (RI), trichloroacetic acid‐soluble nitrogen (TCA‐SN) and organoleptic assessments were analysed. Dry matter and fat values decreased during ripening. Lipolysis level, RI, TCA‐SN values and salt content increased continuously until the end of the ripening period, but total nitrogen decreased throughout a 90‐day storage period. The ripening stage was the main factor affecting the cheese’s sensory properties.     

Hydration,swelling and solubility behaviour of rice in relation to other physicochemical properties

Water uptake at 90°C and above in 16 rice cultivars, representing eight cooking-quality types, showed positive correlation (P≤0.001) with the surface area of the grain, while at 60°C it was negatively related to amylose (P≤0.01), and gelatinisation temperature (P≤0.001), and positively to equilibrium moisture content on soaking (P≤0.001). The swelling and solubility curves for all varieties showed a two-stage swelling pattern. Swelling at 60°C was positively correlated (P≤0.001) with water uptake at 60 and 70°C, while swelling at 70°C, and solubility at 60 and 70°C, showed highly negative correlation (P≤0.001 and P≤0.01, respectively) with water uptake at high temperatures. Waxy rices showed distinct differences from non-waxy rices in their hydration, swelling and solubility behaviour. They swelled more but solubilised less than the non-waxy rices at 96°C.     

湿热处理对大米淀粉理化性质及其米线品质的影响

以大米淀粉为原料,研究湿热处理对大米淀粉理化性质以及米线品质的影响。结果表明:与未处理大米淀粉相比,湿热处理后,大米淀粉的热学特性中T_0、T_P、T_C、T_C_T0、ΔH均增大;淀粉晶型仍为A型,结晶度增加4.14%;淀粉溶解率和膨润力显著降低,直链淀粉含量显著升高;淀粉糊化黏度、衰减值和回生值明显降低;淀粉凝胶硬度、弹性和耐咀嚼性增强;淀粉白度由89.7降低至80.3;添加20%湿热处理大米淀粉制作的米线感官品质和质构特性得到显著改善,断条率和蒸煮损失率分别降低5.67%,10.13%;大米淀粉溶解率、膨润力、溶解率、凝胶特性和糊化特性可有效预测米线品质。     

Effect of ozone treatment on physicochemical properties of waxy rice flour and waxy rice starch

The effect of ozone treatment on physicochemical properties of waxy rice flour and waxy rice starch was investigated. Results showed that ozone treatment increased the pasting viscosity of waxy rice flour. Compared with untreated waxy rice flour, the peak viscosities of waxy rice flour for 0.5, 1 and 2 h of ozone treatments were increased by 27.4%, 32.8% and 45.5%, respectively. The alpha‐amylase in waxy rice flour was inactivated during the treatment. The gelatinisation temperature and enthalpy of waxy rice flour were kept unchanged after the treatment. For waxy rice starch, pasting viscosity, swelling power and molecular weight were increased after 0.5 h of treatment, but decreased as treatment time extended. The ozone treatment decreased gelatinisation temperature and enthalpy of waxy rice starch.     

Salinity alters the protein composition of rice endosperm and the physicochemical properties of rice flour

BACKGROUND: Salinity is one of the major threats to production of rice and other agricultural crops worldwide. Although numerous studies have shown that salinity can severely reduce rice yield, little is known about its impact on the chemical composition, processing and sensory characteristics of rice. The objective of the current study was to investigate the effect of salinity on the pasting and textural properties of rice flour as well as on the protein content and composition of rice endosperm. RESULTS: Rice grown under saline conditions had significantly lower yields but substantially higher protein content. The increase in protein content was mainly attributed to increases in the amount of glutelin, with lesser contributions from albumin. Salinity also altered the relative proportions of the individual peptides within the glutelin fraction. Flours obtained from rice grown under saline conditions showed significantly higher pasting temperatures, but lower peak and breakdown viscosities. Rice gels prepared from the flour showed significantly higher hardness and adhesiveness values, compared to the freshwater controls. CONCLUSION: Salinity can significantly affect the pasting and textural characteristics of rice flour. Although some of the effects could be attributed to changes in protein content of the rice flour, especially the increased glutelin level, the impact of salinity on the physicochemical properties of rice is rather complex and may involve the interrelated effects of other rice components such as starch and lipids. Copyright © 2011 Society of Chemical Industry     

Correlation of physicochemical and nutritional properties of dry matter and starch in potatoes grown in different locations

The physicochemical and nutritional properties of dry matter and starches were studied from 13 potato varieties grown in different locations in Canada. Pearson correlation and principal component analysis were employed to examine relationships amongst variables. Phosphorus content in starch was negatively correlated to rapidly and slowly digestible starch content, while positively correlated to resistant starch content (RS) in raw dry matter and raw starch (p < 0.001). RS content of cooked starch was positively correlated to phosphorus content (0.48, p < 0.01), enthalpy of retrograded starch (0.48, p < 0.01), peak viscosity (0.52, p < 0.001) and breakdown of starch (0.43, p < 0.01). The principal component analysis grouped the 13 potato varieties by growing location, where phosphorus content in starch was the major difference. The results would imply that phosphorus content of starch was a key factor affecting physicochemical and nutritional properties of dry matter and starch in potatoes.     

Effects of germination time on the structural,physicochemical and functional properties of brown rice

Germinated brown rice (GBR) is a gluten-free food raw material. Its tissue structure, physicochemical properties and functional properties depend on the germination time. In this study, rapid viscosity analyses, differential scanning calorimetry and X-ray diffraction et al were used to analyse the structural, physicochemical and functional changes in brown rice (BR) during germination. Gamma-aminobutyric acid (GABA), total phenolic compound, glutathione (GSH) and amino acid contents increased during germination. GBR exhibited the highest GSH (22.70 mg per 100 g) and amino acid (8.02 mg per 100 g) contents at 24 h and the highest GABA content (253.35 mg per 100 g) at 36 h. Furthermore, BR germinated for 36 h showed greater enthalpy (ΔH) than ungerminated BR. Although GBR showed less crystallinity than ungerminated BR, germination did not change the crystalline structure type of starch (A-type). These results inform choices of the appropriate applications of GBR to promote its utilisation in the food industry.