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.     

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.     

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.     

MEASURING HARDNESS DISTRIBUTION OF COOKED RICE BY SINGLE-GRAIN PUNCTURE

A 0.71-mm-diameter punch mounted in the Instron Universal Testing Machine was used to measure hardness of 100 individual grains of 15 rices after cooking. A hardness distribution curve for each rice was obtained. The puncture forces of rices cooked at a fixed water:rice weight ratio of 2 were more variable than those for rices cooked in excess water for the optimum cooking time. High- and intermediate-amylose rices cooked using a water:rice ratio of 2 were harder than corresponding rices cooked in excess water. For waxy and low-amylose rices, the reverse was generally true. Pairs of rices with almost identical physicochemical properties but which differed in preference tests by consumers also differed in their hardness distribution profile.     

CONSUMER PREFERENCE AND PROPERTIES OF RAW AND COOKED MILLED RICE

Consumer preference tests for raw and cooked rices were run on representative consumers 16 years and older in a selected Philippine village. For four sets of samples, major criteria for selecting raw milled rice were grain whiteness and hardness, and aroma and flavor for boiled rice. Actual preference ranks suggested partiality to white raw rice and low-amylose, intermediate-amylose and high-amylose boiled rice in order of decreasing preference. Soft texture due to low amylose content probably contributed to better flavor of boiled rice.
Selection criteria for one set of waxy rices were aroma and whole, big grains for raw rice, and aroma and cohesiveness for rice cake suman sa antala . Properties disliked in suman were flakiness, and coarse, hard, and soft textures. Among five low-gelatinization temperature, waxy milled rices, the traditional, aromatic, coarse-grained Malagkit Sungsong was preferred over newer rices with less aroma and with longer grains in both raw and suman forms.     

INTERNATIONAL COOPERATIVE COMPARISON OF INSTRUMENT METHODS FOR COOKED RICE TEXTURE

The texture of 10 milled rices cooked by a standardized method in excess water was measured in 11 laboratories using various instrument methods that had been developed specifically for national samples. The samples selected represented a wide range of rice textures. Instrument indexes for hardness and stickiness of cooked rice generally were more sensitive than the corresponding taste panel scores in discriminating among the 10 cooked rice samples. Instrument indexes for hardness correlated positively among each other as did those for stickiness. Most hardness indexes showed significant negative correlation with stickiness indexes. Most hardness indexes were positively correlated with amylose content whereas stickiness indexes were negatively correlated with amylose content. The continued use of amylose content as an index of eating quality in a rice breeding program is justified.     

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.     

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.     

紫米与籼米复配比对复配粉性质及紫米粉丝品质的影响

本文通过混配高直链淀粉的籼米粉来改善紫米粉性质,研究复配粉不同配比对原料性质及紫米粉丝品质的影响。将紫米粉与籼米粉按照一定比例进行复配并制作粉丝,以复配粉的直链淀粉含量、溶解度、膨润力、胶稠度、糊化及凝胶特性为理化性质测定指标,以紫米粉丝的蒸煮、花色苷含量及保留率与感官品质为评价指标,得到了优选原料粉复配比例为籼米粉:紫米粉为8:2。在该配比下,复配粉的直链淀粉含量由紫米粉的15.75 g/100 g增加到26.86 g/100 g,溶解度降低为6.24 g/100 g,膨润力减少为6.80 g/g,胶稠度由中软稠度变为硬稠度,低谷黏度、最终黏度与回生值增大,凝胶硬度与持水性增大,粘结性与失重率降低。上述原料性质的变化增强了紫米粉丝凝胶的结构强度,降低了其粘性,优化了其水合性质,最终改善紫米粉丝品质。最适配比下制作的紫米粉丝品质为:复水时间为508 s,断条率为9.67%,蒸煮损失率为34.37%,蒸煮品质与市售米粉丝水平相近,花色苷含量为18.36 mg/100 g,保留率达到65.68%,颜色紫红,带有紫米清香,软硬适中。     

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.     

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).     

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.     

Effect of rice ageing and freeze‐thaw cycle on textural properties of cooked rice (Oryza sativa L.) cv. Khao Dawk Mali 105

This study investigated the effect of rice grain ageing (0.7–12 months) and freeze‐thaw 1–5 cycles on the textural properties of cooked rice. The cooked rice from aged rice grains was freezing and thawing up to five cycles. Ageing of the rice grain increased the hardness and decreased the stickiness of the cooked rice. Repeated freeze‐thaw cycles caused an increase in hardness and a decrease in stickiness of aged cooked rice. Scanning electron micrographs showed a rough surface on the cooked rice after repeated freeze‐thaw cycles, especially for cooked rice from rice aged for 12 months. Differential scanning calorimetry and X‐ray diffraction showed increased starch retrogradation with increased freeze‐thaw cycles. The gelatinisation temperature and gelatinisation enthalpy increased when rice was aged for longer periods. Thus, ageing of rice and the number of freeze‐thaw cycles influence the textural properties of cooked rice.     

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.     

Effect of high-temperature fluidized-bed drying on cooking, textural and digestive properties of waxy rice

In this work, changes of the cooking and pasting properties as well as starch digestibility of waxy rice (RD6) during hot air fluidized bed drying were investigated. Re-moistened waxy rice at an initial moisture content of 28% dry basis (d.b.) was dried at 90-150 °C. Semi-dried waxy rice was tempered and dried again by ambient air until the moisture content reached 16% (d.b). It was found that the degree of gelatinization increased with an increase in the drying temperature. At 130 and 150 °C the appearance of some waxy rice kernels changed from opaque to translucent, indicating complete gelatinization. Thermal degradation of amylopectin granules during high-temperature drying caused the starch to be more rapidly digested; this led to lower peak viscosity and setback viscosity. In addition, waxy rice processed at higher drying temperatures (90-150 °C) could adsorb more water and exhibited larger loss of solids during soaking. Such effects subsequently led to samples with lower hardness and higher stickiness. Based on the sensory analysis results, however, waxy rice dried at the above temperatures, when cooked, did not significantly differ in overall acceptability from the reference waxy rice.     

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。     

Steeping‐induced physicochemical changes of milled waxy rice and their relation to the quality of yukwa (an oil‐puffed waxy rice snack)

The influence of water‐steeping periods (0 to 15 days, 25 °C) on the physicochemical properties of raw waxy rice in relation to the yukwa quality was investigated. The moisture contents in waxy rice and reducing sugar in its steeping medium were increased, while contents of protein and minerals of raw waxy rice were decreased in proportion to the water‐steeping duration. With longer steeping periods, swelling power, solubility and peak viscosity were increased, while grain hardness was decreased with apparent kernel structural change. Depending on the water‐steeping duration of raw waxy rice, the hardness decreased from 26.0 to 1.8 g, and the expansion ratio of yukwa increased from 762 to 1539%. Correlations between the physicochemical properties and yukwa quality indicated that variables having the most positive influential on expansion ratio were reducing sugar (γ = 0.961, P < 0.01) and peak viscosity (γ = 0.897, P < 0.01), and those for hardness of yukwa were crude protein (γ = 0.875, P < 0.01) and hardness (γ = 0.887, P < 0.01) of the steeped waxy rice. It is suggested that steeping‐induced physicochemical changes of raw waxy rice had a significant influence on the final quality of yukwa in terms of hardness and expansion ratio. Copyright © 2004 Society of Chemical Industry     

米饭添加量对大米粉性质及粉条品质的影响

以早籼米为原料制成米饭并将其干燥研磨成粉末分别以5、10、15、20、25、30、35%的比例与生大米粉末混合,通过对大米粉的糊化和凝胶等理化特性以及粉条的蒸煮损失和拉伸性能进行分析,并结合感官评分,研究米饭添加量对大米粉性质及粉条品质的影响。结果表明：不同的米饭添加量糊化特性指标存在显著差异(P<0.05),主要是大米粉的糊化温度与米饭添加量成正比,峰值黏度、衰减值与米饭添加量成反比;其中添加量为15%的大米粉凝胶硬度、弹性、咀嚼性和回弹性最大,均显著(P<0.05)高于其他样品;溶解度和膨胀力则受米饭添加量的影响不显著。在粉条品质方面,米饭添加量≦15%时,随着米饭的添加,粉条的断条率、吐浆值降低,抗拉伸阻力、延伸度增大,感官品质提升;米饭添加量>15%时,则相反。因此,当米饭添加量为15%时,粉条的综合品质最佳。     

基于物性仪评价大米食用品质的方法研究

为了建立国产物性仪评价大米食用品质的方法,探索了米饭摆放方式及压缩参数对大米物性测试结果的影响,并研究了米饭物性仪测试结果与感官评价指标间的相关关系。结果表明：米饭粒在辐射状摆放、圆柱型压缩探头、压缩比70％和压缩速率0．5mm／s的条件下,其物性测定结果重现性较好。物性测试的硬度、弹性和黏硬比与米饭感官评价中软硬发、弹性及综合评分值具有显著的相关性。可见硬度、弹性和黏硬比是米饭物性仪评价米饭食味的关键指标,物性测试仪能代替部分感官评价来快速、准确地测量米饭物性。     

HARDNESS OF COOKED MILLED RICE BY INSTRUMENTAL AND SENSORY METHODS

Fifteen milled rice varieties covering the usual range of amylose content and cooked rice hardness were used in a collaborative study to verify the sensitivity of the present objective method for measuring cooked rice hardness. The grains were cooked either in a rice cooker using a fixed water:rice ratio of 2:1, or by boiling in excess water for the predetermined optimum cooking time for each sample followed by draining. Hardness of cooked rice was measured in an Instron Universal Testing Machine (UTM) using two methods: (1) puncture of 100 individual grains and (2) extrusion through a 30 cm² Ottawa Texture Measuring System (OTMS) cell with either a 3.2- or 4.8-mm-diam. holes plate. Hardness values were compared with sensory scores by a trained panel composed of 11 members. Sensory hardness of the rices cooked in a fixed amount of water showed very good correlation with puncture force (r = 0.94, P < 0.01) and with extrusion force through a 3.2-mm-diam. holes plate (r = 0.94). The correlation coefficient between puncture force and extrusion force was 0.97. Paired comparison test by the sensory panel on three pairs of rices verified consumers' claims with respect to preference between members of each pair and agreed with results of ranking test.