INFLUENCE OF PARBOILING AND FREEZING CONDITIONS ON TEXTURAL PROPERTIES OF CALIFORNIA COOKED RICE

The textural properties of thawed samples of cooked parboiled, long (Cal Belle) and short (S201) grain rice varieties were evaluated using an Instron Universal Testing Instrument (Model 1122). In general, the parboiling treatments resulted in a significant increase of hardness but a significant decrease in stickiness of both long and short grain cooked rice when freezing conditions were pooled. Freezing increased hardness and decreased stickiness of long grain cooked parboiled rice significantly regardless of parboiling conditions, however, it did not decrease the stickiness of short grain cooked parboiled rice significantly. The long grain rice was harder and less sticky than the short grain rice when cooked regardless of treatments used. Hardness was negatively correlated with stickiness indexes (r =?0.819, P < 0.001).     

ELECTROMYOGRAPHIC STUDY ON COOKED RICE WITH DIFFERENT AMYLOSE CONTENTS

The texture of six varieties of cooked rice with different amylose contents was measured with a Texturometer. Masticatory behavior of the rice was evaluated using electromyography (EMG) of masticatory muscles. Differences in mastication patterns among the seven subjects examined were greater than between rice varieties. Masticatory behavior was more related to the adhesiveness and stickiness of rice as measured using a Texturometer than to the hardness. The number of chews and masticatory time, total duration of mastication and total muscle activities were highly correlated with each other, and were greater in cooked rice with a high amylose content, which showed low adhesiveness and stickiness values using a Texturometer. Cooked rice with a high amylose content was masticated with high masseter muscle activities. The ratio of jaw-opening muscle activity to the preceding jaw-closing muscle activity was low in high-amylose varieties, which corresponds to the ratio of stickiness to hardness using a Texturometer. Between-sample differences in mastication parameters were more apparent in the early stage of mastication, and no significant diference was observed in the late stage.     

小麦胚乳中直链淀粉含量分布及其对面条品质的影响

在同一生产线上对同一品种小麦按加工系统取制面粉样品,测定各粉样的直链淀粉含量;选择部分样品在其中添加整个粉路中最具代表性的系统面粉制成的谷朊粉,使各样品蛋白质含量相等、质量接近,在这种的前提下,研究直链淀粉含量对面条品质的影响。研究结果表明,小麦胚乳中,越接近皮层的部位,直链淀粉含量越低;越接近麦心的部位直链淀粉含量越高。小麦胚乳中的淀粉总量与面条品质无明显的相关性,而直链淀粉及支链淀粉含量对面条品质影响较大。直链淀粉含量与面条感官评价的表观状态、适口性、韧性、黏性、光滑性、食味及总评分都呈极显著负相关;与面条的煮制特性的干物质吸水率、蛋白质损失率和干物质损失率呈极显著正相关;而与面条质构仪TPA测定参数的黏合性、硬度和咀嚼性呈极显著负相关。     

Indicators of eating quality for non-waxy rices

Although amylose content is the major determinant of the eating quality of milled rice, varieties of similar amylose content may differ in eating quality. Stickiness of cooked rice, as measured with an Instron food tester, gave a better correlation with amylose content than did hardness. Among rices of similar amylose content (high, intermediate or low) differences in hardness of cooked rice were shown to be generally related to differences in gel, and amylograph consistency, final gelatinisation temperature, or both. A higher rice concentration improved the differentiation among low-amylose samples for gel and amylograph consistency.     

增城丝苗米米饭理化性质与质构特性的相关性分析

选用7份增城丝苗米的原料大米,研究米饭的质构特性,并分析其与大米的热特性、糊化特性和理化指标之间的相关性。结果表明,增城丝苗米原料大米的硬度、粘性的差别较大,而凝聚性、胶粘性、咀嚼性和回复性均较接近。大米直链淀粉含量与米饭质构特性呈显著相关,米饭硬度、粘性与大米淀粉的糊化起始温度呈正相关,与热焓值呈负相关。米饭的硬度、粘性、凝聚性、胶粘性、咀嚼性和回复性与大米淀粉糊化的最终粘度、崩解值呈负相关,与消减值呈正相关,粘性与回生值呈负相关。因此,开发大米配方时, 将直链淀粉含量检测与大米的糊化特性、米饭硬度和粘性测试分析相结合,对于提高大米配方的品质稳定具有重要意义。     

OBJECTIVE TESTS FOR THE STICKINESS OF COOKED RICE

The suitability of a sieve test and an adhesion test as objective tests for determining the stickiness of cooked rice was examined. Six rice varieties, two each from dwarf incica, tall indica and japonica classes, and stored for 1 and 2 years at three different temperatures, were used. The consistency of the cooked rices was also determined by the Haake consistometer. The sieve test gave a very good indication of the stickiness of cooked rice. The adhesion test also gave a fair indication, but the correlation was less sharp and the test needs improvement. Consistency of cooked rice was negatively correlated with its stickiness. The water-insoluble amylose content of rice seemed to be importantly related to its stickiness and consistency after cooking.     

Cross‐cultural comparisons between Korean and U.S. adults with respect to texture perception and acceptance of cooked milled rice

This study aimed to determine whether texture perception and acceptance of cooked rice could differ with cultural background, especially between Korean and American participants. Participants evaluated eight cooked rice samples with respect to intensities of textural attributes such as visual stickiness, hardness, stickiness and chewiness. Participants also rated the acceptability of and familiarity with those samples. Results showed that Americans gave higher ratings to cooked rice samples with respect to visual stickiness, stickiness and chewiness, while Koreans gave higher ratings to hardness than their counterpart. For Americans, chewiness was considered as a negative driver; whereas for Koreans, visual stickiness and stickiness were identified as positive drivers of overall liking for cooked rice samples. Moreover, a familiarity level of cooked rice samples was a pronounced positive driver of liking for both American and Korean participants. In conclusion, our findings provide empirical evidence that cultural background influences texture perception and liking of cooked rice.     

Importance of insoluble amylose as a determinant of rice quality

Thirty-two varieties of rice, belonging to various classes and characteristics, were studied for their textural and physicochemical properties. The varieties could be divided into five groups depending on their total and hot water-insoluble amylose contents. It was found that the textural properties of the samples (stickiness and consistency of cooked rice and viscogram characteristics) could not be explained on the basis of the total amylose content alone, but they correlated well with the insoluble amylose content. As the insoluble amylose increased, the consistency and the setback increased, and the stickiness and breakdown decreased. The alkali degradation type of rice, and the equilibrium moisture content attained by it after soaking in water, also seemed to have an important relationship with its quality. Neither the protein content nor the gelatinisation temperature, or its various manifestations, seemed to have any relationship to the other quality characteristics studied.     

Potential Influence of a Starch Granule-associated Protein on Cooked Rice Stickiness

The amount of a 60 kdal starch granule-associated protein, or waxy gene product, found in milled white rice was examined in relation to cooked rice stickiness. For 32 rice selections the correlation coefficient was similar though slightly lower for the 60 kdal protein and stickiness (r=?0.85, P<0.01) compared to amylose and stickiness (r=?0.87, P<0.01). The 60 kdal protein content correlated highly with amylose content (r = 0.96, P<0.01), suggesting a more clear association between amylose and texture. However, a possible role for the protein was postulated based on previous work that showed increased stickiness following protein disruption. The gelatinization properties of the starch granule may be influenced by the relative amount of granule-associated protein.     

TEXTURE CHANGES AND STORAGE OF RICE

Monthly texture assessments of seven milled rices, differing in amylose content and stored at 28–30°C, verified that three months was the minimum storage period for major changes to occur in hardness of cooked rice, gel consistency, and amylograph viscosity values. Therefore, texture measurements should be done on samples aged at least three months after harvest. Texture changes tend to be greatest for high-amylose rice with hard gel consistency and least for waxy rice. Free fatty acids were highest in stored, waxy, milled rice. Storage under nitrogen instead of air had a slight retarding effect on storage changes of five rices in another study. Surface defatting with petroleum ether had little effect on storage change in cooked rice hardness and stickiness, but reduced the changes in gel consistency and amylograph setback and consistency.     

MAJOR FACTORS AFFECTING COOKED MILLED RICE HARDNESS AND COOKING TIME

A study was made of factors affecting cooking time and the relationship between water:rice ratio (water content) in the rice cooker method and Instron hardness of cooked rice using 10 milled rice samples of diverse properties. Water:rice ratio for acceptable soft texture (< 10 kg hardness) increased with increasing amylose content of the sample from 1.1 (56% water in cooked rice, wet basis) to 1.9 (68% water). The spread in cooked-rice hardness values was higher at a water:rice ratio of 1.9 (68% water) than at 2.65 (75% water), which was equivalent to the water content of rice cooked in excess water for an optimum cooking time. Cooking time correlated better with starch final gelatinization temperature (r=0.75*) than with surface area per gram (r=−0.49) confirming the results of earlier kinetic studies that cooking rate was mainly influenced by the reactivity of the grain constituents with water.     

不同品种大米理化性质及其淀粉结构对米饭食用品质的影响

米饭食味值和质构特性是评价大米食用品质的重要指标,为了探究不同品种大米的食味值、质构特性与其理化性质及淀粉结构的关系,以12种大米为研究样本,测定其食味值、质构特性、理化性质及淀粉结构特性,并分析内在相关性。结果表明,直链淀粉含量（质量分数）与米饭的硬度呈极显著正相关（P<0.01）,与米饭的凝聚性呈极显著负相关（P<0.01）;米饭食味值、质构特性与大米淀粉的糊化特性、热特性之间存在显著相关性,与结晶特性、淀粉颗粒表面有序度无显著相关性,表明淀粉的糊化特性决定了米饭的食味值、硬度、凝聚性和回复性。该研究可为后期优质稻米筛选培育以及大米适宜性加工提供理论基础。     

SENSORY AND INSTRUMENTAL EVALUATION OF TEXTURE OF COOKED AND RAW MILLED RICES WITH SIMILAR STARCH PROPERTIES

Three pairs of milled rices with similar starch properties (low gelatinization temperature waxy, and low gelatinization temperature low amylose, and intermediate gelatinization temperature intermediate amylose) were assessed for cooked rice properties by two industry taste panels and for raw and cooked rice properties by 30-member Filipino consumer panels. Only slight differences in texture within pairs were noted by the two industry taste panels who had not been trained to assess boiled raw rice or waxy rice. The Filipino consumer panel gave significantly higher ranked scores for one low-amylose variety in both raw and cooked forms. Malagkit Sungsong suman sa antala was ranked higher than modern waxy rices. Instrumental methods for translucency and whiteness of raw rice and Instron hardness and stickiness of cooked rice were not able to detect differences perceived by the Filipino consumer panels.     

施氮量和直播密度对稻米食味品质和淀粉结构的影响

为了明确直播条件下软米粳稻与常规粳稻食味品质与淀粉结构差异特征及其对氮肥和密度的响应变化.本研究以软米粳稻南粳9108和常规粳稻丰粳3227为供试材料,设置3个施氮量(0、150和300 kg hm-2)和3个密度(90×104、180×104和360×104 hm-2),研究施氮量和密度及其互作对水稻食味品质和淀粉结...     

Influence of free‐air CO2 enrichment (FACE) on the eating quality of rice

Rice plants (Oryza sativa L cv Akitakomachi) were grown under free‐air CO₂ enrichment (FACE) in farmers' fields in Shizukuishi, Iwate, Japan during 1999 and 2000. The grains were harvested and subsequently analyzed for protein and amylose contents as well as the traits related to cooked‐rice viscosity. The cooked rice was also subjected to sensory evaluation. The protein content of rice grains grown under elevated CO₂ was significantly lower than that of rice grown under ambient conditions. In addition, CO₂ enrichment increased the whiteness of the grains in both brown and milled rice and reduced their surface hardness. Although the amylose content of rice grains was unaffected, starch pasting properties demonstrated that rice grains in elevated CO₂ had higher maximum viscosity and breakdown than those grown in ambient conditions. Sensory evaluation of cooked rice with respect to umami (deliciousness), appearance, aroma, hardness, stickiness and overall palatability index indicated that the sensory properties were not significantly altered by the CO₂ enrichment treatment. Therefore, we conclude that the growth of the rice cultivar Akitakomachi under elevated CO₂ concentration decreased the protein content, but did not change the palatability to a level that may be detected by sensory taste panel evaluation. Copyright © 2005 Society of Chemical Industry     

大米理化特性与米饭口感品质的相关性研究

本试验以8种原料大米为试验材料,测定了包括水分、脂肪、直链淀粉和蛋白质含量的4项成分指标,采用质构仪对米饭的质构特性进行测定,通过感官评价对米饭的口感品质进行了评定,分析了各成分指标对米饭口感的影响,就米饭的质构特性与米饭的口感品质进行了相关性分析。得出结论：水分、直链淀粉与蛋白质含量对蒸煮质构特性有显著影响;质构指标总体上可以反映人们对米饭口感的评判。     

TEXTURE MEASUREMENT OF COOKED RICE AND ITS RELATIONSHIP TO THE EATING QUALITY

A method has been developed for quantifying hardness, stickiness and cohesiveness of rice. It utilizes the Texturometer and requires only a small quantity of cooked kernels. The portability of rice in Japan is governed by its hardness and the ratio of stickiness to hardness. A texturogram has been constructed showing zones of acceptability as a function of hardness and stickiness. For the non-glutinous rice to be of high acceptability, the ratio of stickiness to hardness should be between 0.15 and 0.20. The developed testing method and the constructed texturogram were used to demonstrate factors affecting the texture of cooked commodity rice, to describe the textural characteristics of convenience rices and to develop some principles on combining different rice varieties for optimum blend texture.     

非发酵型米粉的品质评价体系

本论文以１０种不同的大米（２种粳米,８种籼米）为原料,对其制备的米粉（切粉和榨粉）分别采用感官评定、测定米粉力学性质和烹煮性等方面进行品质评价,提出非发酵型米粉品质评价体系。实验结果表明,仪器测定的硬度与感官评定中的粘性有高度显著的负相关关系;抗拉强度和最大分别与感官评定的筋道感有显著正相关关系;最大应变与感官评定的综合评价有显著正相关关系;因此,在不便采用感官评定的情况下,可用仪器测定的结果预测     

SENSORY TEXTURE PROFILE, GRAIN PHYSICO-CHEMICAL CHARACTERISTICS AND INSTRUMENTAL MEASUREMENTS OF COOKED RICE

Three samples of raw-milled rice, and 4 differently parboiled rices were used to study and to relate sensory perception to instrumental measurements. Variance analysis showed that some physico-chemical characteristics indicated great differences among rice samples: thickness of cooked grain, length/width ratio, water uptake, elastic recovery, white core rate and amylose and protein contents. The most discerning sensory attributes were: elasticity, stickiness, pastiness, mealiness, length of grain, firmness, crunchiness, time in mouth, brittle texture and juiciness. The correlation circle of the principal component analysis (PCA) showed high correlation between some sensory characteristics and instrumental measurements. Melting texture, surface moistness, juiciness, were positively correlated with water uptake (r = 0.70, 0.61, 0.71). Granular texture, crunchiness, brittleness and mealiness were significantly affected by white core presence (r = 0.81, 0.74, 0.86, 0.83). Elasticity was dependent upon elastic recovery and firmness measured by the Viscoelastograph, but not linearly. Length of cooked grain was correlated with the length/width ratio of raw grain (r = 0.83). Pastiness, compactness, stickiness were slightly influenced by the thickness of raw grain (r = 0.81, 0.67, 0.72). To a weaker extent, the sensory firmness was associated with the firmness measured by extrusion force using an Ottawa cell (r = 0.58). PCA showed greatdifferences in texture between rices. Two of the parboiled rices were very elastic, another was firm, granular, crunchy and mealy. The remaining two, cooked longer, were moister and more melting. Among the 3 samples of raw-milled rices, differences in grain length feeling and melting-granular-brittle characteristics. were distinguished.     

米粉干直链淀粉含量与产品感官品质的关系

目的 探究米粉干原料特性对米粉干加工品质的影响, 改进生产工艺水平。方法 采集制作米粉干的主要原料及市场占有率较高品牌的米粉干, 分析其直链淀粉的含量, 并测定煮熟米粉干的耗时、断条率, 评价软硬度、撑盘性、泡发性、糊汤度和黏性感官品质指标。结果 米粉干原料中直链淀粉含量与米粉干的品质存在密切的相关性, 同煮熟耗时呈显著线性正相关, 同断条率呈显著线性负相关, 并同评价指标也呈显著正相关。结论 米粉干原料中的直链淀粉含量直接影响米粉干的感官品质, 生产企业可通过合理搭配产品原料, 实现按需生产。