Changes in volatile aroma compounds of organic fragrant rice during storage under different conditions

BACKGROUND: Aroma of fragrant rice greatly affects palatability as well as consumer acceptability. Loss of desirable volatile compounds such as 2‐acetyl‐1‐pyrroline (2‐AP) and increase in volatile lipid oxidation products in aged rice have been reported. The aim of this study was to monitor the changes in key volatile compounds of organic red fragrant rice cv. Hom Daeng during storage. Effects of packaging material, storage temperature and time were evaluated using solid phase microextraction/gas chromatography/mass spectrometry. RESULTS: Thirteen key volatile compounds including ten lipid oxidation products were monitored. For samples vacuum packed in Nylon/LLDPE pouches at ambient temperature, significant increases in hexanal, 2‐pentylfuran, 1‐octanol and 4‐vinyl guaiacol and significant decreases in 2‐AP and geranyl acetone were found after the second month (P?0.05). Vacuum packing in OPP/Al/LLDPE pouches or storage at 15 °C better retarded the formation of volatile lipid oxidation products and greater retained desirable odorants, including 2‐AP. However, accumulation of lipid oxidation products and 4‐vinyl guaiacol was apparent after the sixth month under these storage conditions. CONCLUSION: A greater extent and higher rate of undesirable changes in volatile compounds were found in samples stored under Nylon/LLDPE/ambient temperature condition. Nevertheless, this condition is acceptable for the retail trade of organic rice in Thailand. Storage conditions using reduced temperature or better packaging materials may be more appropriate for exported rice or superior‐grade fragrant rice to better maintain the desirable rice aroma. Copyright © 2010 Society of Chemical Industry     

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.     

Chemical,functional and physicochemical properties of flour from cassava stored under freezing

Cassava root spoils rapidly after harvest but can be well preserved by storing under freezing. This study investigated the functional, chemical and physicochemical properties of flour produced from frozen cassava roots. Freezing period did not significantly (p < 0.05) alter the moisture, ash, fat and fibre, but had slight effect on the carbohydrate and protein contents of the flour. Lightness, yellowness index and bulk densities of the flour samples reduced with freezing period. While freezing did not significantly (p < 0.05) change the ability of the flour samples to absorb oil, a slight but significant increase in the water absorption capacity was observed. Potassium (1.29–3.46 mg/kg), sodium (1.24–1.28 mg/kg), and calcium (0.94–1.34 mg/kg) were the major minerals in the cassava flour samples. The cyanide content (10.80–22.95 mg/kg) reduced as freezing days increased but peak, setback, breakdown and final viscosities did not follow a particular pattern. The information from this study is important to further determine the industrial potentials of flour from stored cassava roots.     

Effects of three reducing agents on pasting properties of stored rice

The effects of three reducing agents (dithiothreitol, ascorbic acid, and tea polyphenols) on pasting properties of fresh and aged rice were investigated using Rapid Visco Analyzer. Results showed that ascorbic acid did not only significantly increase peak viscosity (PV) and breakdown of aged rice in a concentration dependent manner (p<0.05), but also decreased its setback significantly (p<0.05). Dithiothreitol increased the PV, breakdown and setback of the aged rice. Importantly, the extent of ascorbic acid enhancing PV of the aged rice was higher than that of dithiothreitol, and showed positive dose‐effect relationship. Compared with ascorbic acid and dithiothreitol, tea polyphenols only significantly decreased setback of the aged rice (p<0.05). It was concluded that ascorbic acid was the most effective improver on pasting properties of aged rice as compared to dithiothreitol or tea polyphenols, especially in increasing PV and breakdown, and in decreasing setback. This showed rice ageing included, but was not limited, to the formation of disulfides, and more changes of ageing would involve hydrogen bonding and hydrophobic interactions. The different influences of SDS on fresh rice and aged rice also confirmed these findings to a certain extent. The improved role of ascorbic acid was ascribed to enhancing water absorption capacity, soluble solid content and granule swelling capacity of the aged rice.     

Changes to physicochemical properties and aroma of irradiated rice

Gamma-irradiation at dosages of 0.2-2.0 kGy controlled insects in packaged aromatic milled rice (KDML-105). However, it induced changes in physicochemical properties of the rice. Decreases in some pasting parameters, increases in water absorption and total solids in cooking water, and decreased cooked rice hardness showed that starch granules of milled rice were changed by irradiation. Alterations of the granular structure of starch were seen by scanning electron microscopy. These changes affected the texture of the cooked rice. In addition to an increase in yellowness (b-value) and an increase in lipid oxidation (TBA, thiobarbituric acid) and a decrease in volatile compounds (ACPY, 2-acetyl-1-pyrroline), irradiation contributed to changes in the colour and aroma of irradiated cooked rice. Gamma dosage had a significant positive correlation (P<0.01) with the b-value, pasting properties and a negative correlation with cooked rice hardness and ACPY content. Panelists responded to these changes with less perception of sensory qualities. Maximum doses of less than 1.0 kGy should be used to disinfest aromatic rice although when considered strictly on aroma, less than 0.5 kGy would be more suitable.     

Changes in physicochemical characteristics of rice during storage at different temperatures

This study investigated the changes in the physicochemical properties of rice during storage at different temperatures. Milled rice stored at high temperatures showed higher fat acidity than rice stored at low temperatures. Although the moisture content of milled rice stored at 30 °C and 40 °C decreased below 15.5% (15.33% and 15.22%, respectively) after 1 month, adequate values were maintained with storage at 4 °C for 3 months (15.50%) and at 20 °C for 2 months (15.53%). Rice stored at low temperatures retained its white coloration, whereas low color retention values were obtained at higher storage temperatures. Peak viscosity increased during 4 months of storage and larger changes were found at higher storage temperatures. Breakdown decreased and setback increased with storage, regardless of storage temperatures. Storage at higher temperatures increased cohesiveness and hardness in compared with storage at lower temperatures. High temperatures also led to a decrease in adhesiveness with age. High temperatures (30 °C and 40 °C) significantly decreased all sensory values even after 1 month of storage. These results are similar to those obtained in an analysis of cooked rice texture. The results of this study indicate that storage temperature is an important factor affecting the physicochemical properties of rice. Short storage periods below room temperatures are recommended to maintain rice quality.     

贮藏过程中酸败引起的米糠谷蛋白功能性质变化

将新鲜米糠在25℃、相对湿度85%的条件下贮藏不同时间得到不同酸败程度米糠,随后脱脂制备米糠谷蛋白,研究米糠酸败对米糠谷蛋白功能性质的影响。结果表明:米糠谷蛋白羰基含量随贮藏时间延长而增加,表明米糠谷蛋白在贮藏过程中发生了氧化;随着贮藏时间的延长,米糠谷蛋白溶解性下降了40%;米糠谷蛋白持水性、持油性、起泡能力、泡沫稳定性、乳化性和乳化稳定性则随着贮藏时间延长均先上升后下降,其中持水性和持油性分别在贮藏3d和1d后达到最大值,分别为212.61%和657.25%;起泡能力和乳化性均在贮藏1d后达到最大值,分别为75.06%和76.27m2/g,泡沫稳定性和乳化稳定性则在贮藏3d后达到最大值,分别为69.30%和20.60min。表明米糠短期贮藏可提高谷蛋白功能性质,而长期贮藏则会降低。     

Soybean seed storage: Packaging technologies and conditions of storage environments

Artificial refrigeration is sufficient for maintaining the quality of soybean seeds in storage in processing plants, but when lots are distributed to rural producers, they are often kept in natural environments, without temperature or relative humidity control, which decreases their germination rates. This research aimed to evaluate different storage conditions and technological packaging for soybean seeds. The first stage evaluated the quality of soybean seeds stored at different temperatures for up to one year in raffia bags with or without polyethylene inner liners. The second stage evaluated the quality of soybean seeds stored in a natural atmosphere in raffia or laminated packaging, in a modified atmosphere with polyethylene packaging, in a refrigerated atmosphere with raffia or laminated packaging, or in a modified and refrigerated atmosphere with polyethylene packaging. An increase in storage time had a negative influence on the quality of the stored seeds. Storage temperature was the main influence in the reduction in seed physiological quality. Storage of soybean seeds in raffia packaging coated with polyethylene in a natural-temperature environment resulted in seeds retaining similar physical and physiological qualities to those stored under refrigeration. Raffia packaging coated with laminated material maintained the best physical and physiological quality of soybean seeds stored over time. Optimal packaging technology with laminated coating in “big bag” format has replaced the conditioning of storage environments with the maintenance of the quality of soybean seeds over time. The packaging technology is an excellent alternative for the soybean processing units.     

Underlying reasons for waxy rice flours having different pasting properties

The underlying reasons for three waxy rice varieties, Yang-fu-nuo (Y), Su-yu-nuo (S), and Guang-ling-xiang-nuo (G), having different flour pasting properties were examined. The pasting properties of the isolated waxy rice starches did not correlate with those of the corresponding waxy rice flours. Examining the pasting properties of the flours in 0.5 mM AgNO₃ solution, treated with dithiothreitol and protease, suggested that rice protein and amylase activity were the main causes of the pasting property differences among the rice starches and flours. Starch isolated from Y flour had a larger proportion of A and B₁ chains, longer average chain length and longer exterior chain length, which explained its higher gelatinisation temperature, higher pasting consistency, greater extent of retrogradation, and the firm texture of cooked Y rice.     

贮藏过程中米谷蛋白纤维聚集体理化性质变化规律

目的：探究贮藏时间与不同加热时间下米谷蛋白纤维聚集体(Rice glutelin fibril aggregates,RGFAs)溶液功能特性之间的关系。方法：以米谷蛋白(Rice glutelin,RG)为原料,在85 ℃、pH 2.0的条件下加热2~15 h制备得到RGFAs,在4 ℃下分别贮藏1 d和4 d,测定不同RGFAs样品的表面疏水性、乳化性、剪切黏度、RGFAs-淀粉混合物糊化特性及水解率。结果：在低温贮藏4 d后,乳化性得到明显改善;热处理2~10 h形成的RGFAs溶液的表面疏水性显著降低(P＜0.05),而15 h热处理后形成的RGFAs溶液表面疏水性无显著变化(P＞0.05),同时15 h-RGFAs溶液体系的剪切黏度降低。贮藏1 d的2 h-RGFAs与淀粉混合物的糊化温度最低(83.98±0.08) ℃,且贮藏1 d的RGFAs样品与小麦淀粉混合物的水解率更低。结论：贮藏1 d的RGFAs样品对小麦淀粉的水解抑制作用优于贮藏4 d的RGFAs样品。     

Differences in physicochemical properties of kernels of two rice cultivars during grain formation

BACKGROUND: Rice varieties with similar apparent amylose content may have different grain qualities. The development of rice quality is a dynamic process that occurs with the formation of rice kernels. In this study, physicochemical properties during the grain formation period were investigated to interpret differences in grain quality between two non‐waxy rice cultivars, Wuyujing3 and 30you917, with similar apparent amylose content. RESULTS: There were significant differences in dynamic changes in 1000‐grain weight, amylose content and pasting and thermal properties during grain formation of the two cultivars. The difference in their apparent amylose contents from 5 days after anthesis (DAA) to 15 DAA was significant, except in the late grain‐filling stage. Wuyujing3 showed a slower increase in 1000‐grain weight than 30you917 from 10 to 25 DAA. The transition temperatures (T_o, T_p and T_c) of developing grain flour of Wuyujing3 were higher than those of 30you917 during the grain formation period. Wuyujing3 showed greater stickiness (higher breakdown and peak viscosity and lower positive setback) than 30you917 according to Rapid Visco Analyser (RVA) profiling. CONCLUSION: The results suggested that the differences in cooking and eating quality parameters of the two mature rices were determined by the differences in grain filling and the dynamic changes in the main rice quality components such as amylose content, grain weight and differential scanning calorimetry and RVA properties, which will help cultivators understand the physical basis of rice quality development. Copyright © 2011 Society of Chemical Industry     

不同地区不同储存条件对储粮“热皮”厚度的研究

粮食在储存过程中,粮温随仓温、气温变化。春夏演替过程中,粮温表现为"热皮""冷芯",粮堆产生温度梯度。实际工作中,粮情测温电缆行列间距通常在4～5 m,边缘测温点距粮面、仓底和仓壁0.3～0.5 m,无法准确反映"热皮"处粮情状况。本实验旨在研究"热皮"厚度范围,为制定粮仓保温措施提供参考。     

Effects of freezing rates on starch retrogradation and textural properties of cooked rice during storage

The effects of freezing rates and storage temperatures on starch retrogradation and textural properties of cooked rice were evaluated. Cooked rice was frozen with different freezing rates and then stored at 4 °C for 14 days or −18 °C for up to 7 months. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by a differential scanning calorimetry, and textural properties were determined by a texture analyser. The results showed that the ΔH_r and hardness values had a negative correlation with freezing rate, however, a positive correlation was found between adhesiveness and freezing rate. On the other hand, the advantages (lower hardness and higher adhesiveness, less starch retrogradaton) of cooked rice gained by rapid freezing, were lost quickly in the first 3 days of storage at 4 °C. However, rapid freezing combined with −18 °C frozen storage can effectively retard starch retrogradation and maintain the textural properties of cooked rice for at least 7 months. Therefore, high quality cooked rice can be produced by combined rapid freezing with frozen storage.     

Quality changes of burnt aromatic coconut during 28-day storage in different packages

The shelf-life of unwrapped, film-wrapped and vacuum-packed burnt aromatic coconut was studied at 5±1 °C and 80-90% relative humidity. Regardless of the packaging treatments, weight loss of whole burnt coconut increased with storage time. Transmittance and lightness (L*) values of coconut water decreased (P<0.05) with longer storage time. The pH of coconut water and coconut meat from the vacuum-packed treatment decreased as storage time increased. Sensory analysis showed that, for all treatments, the yellowness intensity of coconut water increased whereas its transparency decreased with time. The sourness intensity of vacuum-packed coconut water increased on later days of storage. Only the film-wrapped coconut, having the shortest shelf-life, had mold on its shell and husk at the end of storage. This study showed that the unwrapped, film-wrapped and vacuum-packed burnt coconuts could be stored for up to 14, 18 and 28 days, respectively, under the conditions used in this study.     

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。      

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。      

Effect of ageing-induced changes in rice physicochemical properties on digestion behaviour following storage

The changes in rice grains structure and digestion behaviours were investigated following storage at 4 °C and 37 °C, respectively. Pasting study indicated that rice samples stored at 37 °C demonstrated a consistent increase in the time to peak viscosity of the Rapid ViscoAnalysis parameters, implying a quick ageing progress. Compared to the rice stored at 4 °C, aged rice (stored at 37 °C) showed a coarser morphology after cooking by SEM, suggesting a limited starch gelatinization. Consistently, ageing process led to a decrease in the leaching of starch molecules in cooking residual water, which further confirmed that starch granules in aged rice grain caused less hydration and swelling. The analysis of the amount of cell wall remnants showed that rice stored at 37 °C caused a significant increase in the amount of cell wall remnants along the storage at 37 °C, which might suggest that the cell wall structure of the rice grains became more lignified because of the ageing. Furthermore, the ageing process significantly reduced rice digestion kinetics both in rate and extent. Thus, it is assumed that ageing process leads to the cell walls becoming more strengthened and lignified, which makes the rice grain more organized in its structure, and subsequently reduces starch granules disruption and molecules leaching during the cooking. Therefore, this study suggests that the changes in digestion behaviours of rice are highly associated with the changes in rice physical and chemical properties occurred during storage and the ageing process might be another option for manipulating rice digestion properties.