Development And Validation Of Auto Measurement System For Hardness And Viscosity Of Cooked Rice

With the rapid development of economy and elevation of living standard in China, high quality rice is being required by more and more domestic consumers. However, most of the indicators or indexes in current standards regarding taste quality, a key criterion to rice quality as whole, were assessed and evaluated organoleptically or were based on conventional physical and chemical measurements, which limited the improvement of rice quality due to subjectivity, low accuracy and time-consuming of existing measurements. The expression, measurement and relevant techniques are preconditions in evaluating rice quality. Therefore, focused on taste quality, establishment of new methodology for the expression and measurement of hardness, viscosity and textural property of cooked rice and development of new method and apparatus for simple, rapid and accurate measurement of rice quality, based on the understanding of rice quality properties and by means of principles and analytical techniques in mechanics, are of great importance in improving the China’s standardization of rice quality. In this study, the measurement mechanisms for textural properties of cooked rice were investigated based on the smallness of rice grains in size, displacement and force. The methodology and relevant measuring techniques which fit the textural properties of cooked rice were established, and the quantitative expression of rice textual properties (e.g. hardness) was actualized. Furthermore, the accuracy and applicability of the auto measurement system were validated through the instance evaluation of factors affecting rice taste properties including rice varieties, fertilizer application level and transplanting methods, and observation of inner microstructure of crystal particles in cooked rice. Main results obtained in the study showed as following:1. An auto measurement system which can meet the requirements of high precision and sensitivity in hardness and viscosity assessment for cooked rice was developed in this study, based on textural properties and material characteristics of cooked rice and principles and methods for measuring mechanical properties of the materials including organic solids and metals. The hardware of the system included subsystem of double cantilever for stress-strain measurement, auto driving device, data card, power unit and tank body, while the software contained running process control module, data analysis module, data processing module, data management module and man-machine interface. The hardware and software were well designed, optimized and integrated. The system can directly load/unload rice grains and automatically measure hardness and viscosity of cooked rice.2. Based on analyzing the characteristic parameters in deforming force distribution curve, the slope values in force-displacement loading/unloading curve, which well reflected rice texture parameters, were chosen to quantitatively express the hardness and viscosity of cooked rice. We also standardized the mean values of the slopes in loading/unloading curves and used real number0-10to represent the hardness and viscosity of cooked rice. The system can identify the difference of hardness and viscosity between rice varieties and the change of hardness and viscosity with storage time of cooked rice. The accuracy and applicability of the system was verified by comparing with the rice grain taster analyzer, Japan.3. Through measuring samples from different varieties, fertilizer application levels and cultivation methods, The accuracy and applicability of the system was fourthly validated:1) The degree of hardness and viscosity of51rice varieties tested using the system ranged from7.07to7.75and7.70to8.17, respectively. Based on hardness,51varieties were clustered into4types:first type included9varieties (e.g. Zhendao210), its hardness varied between7.07-7.28; second type included16varieties (e.g. Zhendao158), its hardness varied between7.29-7.44; third type included18varieties (e.g. Wujing13), its hardness varied between7.44-7.56; fourth type included6varieties (e.g. Changjing09-8) its hardness varied between7.59-7.75. Based on hardness,51varieties were clustered into4types:first type included7varieties (e.g. Wu28181), its viscosity varied between7.70-7.79; second type included14varieties (e.g. Changyou2), its viscosity varied between7.82-7.91; third type included19varieties (e.g. Zhendao158), its viscosity varied between7.93-8.0; fourth type included11varieties (e.g. Zhendao158), its viscosity varied between8.02-8.17. Based on both hardness and viscosity,51varieties were also clustered into4types, in which hardness increased in pace with viscosity; and4varieties (e.g. Zhendao210),14varieties (e.g. T721),27varieties (e.g. Taijing394) and6varieties (e.g. Changjing09-8) were included in four types (1-4). respectively.2) The response of hardness and viscosity of different varieties to N rate fitted quadratic equation, and the maximum hardness and viscosity appeared when17.5kgN/666.7m2was applied.3) Hardness and viscosity of cooked rice responded to transplanting method. The order for hardness was:drought direct seeding> hand transplanting> wet direct seeding> machine transplanting> seedling scattering> machine drilling> seedling scattering with no tillage. The order for viscosity was:hand transplanting> drought direct seeding> wet direct seeding> machine transplanting> seedling scattering with no tillage seedling> machine drilling> seedling scattering.4. By means of metallographic analysis we used electronic microscope (X400) to observe the inner structural properties including size, distribution and linkage between crystal particles for the samples from rice varieties under different N application rates. The results showed that hardness and viscosity were high when crystal particles were small in size and tight in arrangement, which provided further evidence for validating the accuracy of the system. Hardness and viscosity measured by the system could reflect the inner organization and structural property of cooked nce.In conclusion, the expression and automatic measuring system developed in this study can visually reflect hardness and viscosity of cooked rice. The system also overcomes the shortages in current instruments (e.g. rice grain taster analyzer, Japan) based on optic principles which can be affected by protein and amylose in cooked rice. Meanwhile, the system fits the expressions and habits in hardness and viscosity measurements and provided a simple, accurate and reliable approach for the evaluation of rice taste quality.