คุณภาพของข้าวหอมใบเตยและผลิตภัณฑ์ข้าวพร้อมบริโภคระหว่างการเก็บรักษา

Abstract

Hom Bai Toei rice (Cultivar 85) is specific-pandan flavour rice from Thailand that has soft texture when it was cooked. Hom Bai Toei rice can be consumed either in a form of brown or milled rice. After harvested, paddy rice is dehydrated by sun light to reduce the moisture content until its reached 14% or below. Then, paddy rice is dehulled to obtain brown rice. Furthermore, brown rice is removed bran and germ to obtain milled rice. The quality of cooked rice was affected by rice and water ratio and also the duration of aged rice. At present, ready-to-eat foods are of important and the market share has been increased rapidly. Since people do not have time for cooking. Therefore, this research was to study the effect of storage time on the rice quality, rice to water ratio on cooking quality as well as to investigate the sterilization process to produce ready-to-eat rice in a retort pouch and to monitor the quality of cooked rice during storage. Fresh Hom Bai Toei brown and milled rice was packed in Nylon/LLDPE plastic bag under vacuum and non-vacuum packaging and storaged at room temperature for 6 months. Each month, Hom Bai Toei brown rice and milled rice grain was determined for physical, chemical and physicochemical properties. It was found that the properties of Hom Bai Toei brown and milled rice that was kept under vacuum and non-vacuum packaging changed during storage (p<0.05). Hom Bai Toei brown rice that was kept under vacuum packaging had lower rancidity than the one that was kept under non-vacuum packaging during storage (p<0.05). The thiobarbituric acid value (TBA) of fresh Hom Bai Toei brown rice was 0.55 mg of malonaldehyde/kg sample, while the TBA values of non-vacuum and vacuum Hom Bai Toei brown rice that was stored for 6 months were 1.15 and 0.97 mg of malonaldehyde/kg sample, respectively. In addition, the TBA values of fresh Hom Bai Toei milled rice was 0.46 mg of malonaldehyde/kg sample, while the TBA values of non-vacuum and vacuum Hom Bai Toei milled rice that was stored for 6 months were 1.07 and 0.84 mg of malonaldehyde/kg sample, respectively. Hexanal that acts as a main volatile oxidative product increased during storage (p<0.05). While, the specific pandan flavor compound, 2-acetyl-1-pyrroline (2AP) decreased during storage (p<0.05). The peak viscosity, final viscosity and setback viscosity of Hom Bai Toei brown and milled rice that was kept under non-vacuum and vacuum packaging decreased during storage (p<0.05) with an increasing of crystallinity and enthalpy of gelatinization during storage (p<0.05). The effect of rice to water ratio on the quality of cooked rice either fresh or stored Hom Bai Toei brown and milled rice were investigated. Fresh Hom Bai Toei brown and milled were packed in a Nylon/LLDPE plastic bag under vacuum packaging and stored at room temperature for 6 months (Stored rice). Fresh and stored brown rice (the 6th month) were cooked with rice cooker by using various ratios between rice and water (1:1.5, 1:2 and 1:2.5 w/w). Meanwhile, fresh and stored milled rice were cooked by using various ratios between rice and water as 1:1, 1:1.5 and 1:2 w/w. The suitable ratio between rice and water was selected according to the sensory evaluation score (9-point Hedonic scale). The result showed that appearance, colour, flavour, texture, taste and overall liking scores of stored Hom Bai Toei brown and milled rice were higher than the fresh rice (p<0.05). In addition, the stored Hom Bai Toei brown rice with the ratio of 1:2.0 (rice: water) and stored Hom Bai Toei milled rice with the ratio of 1:1.5 (rice: water) was selected. This was due to the highest score in appearance, texture and overall liking scores (p<0.05). The hardness and adhesiveness of stored Hom Bai Toei brown rice were 54.81 and 2.61 N, respectively. While, the hardness and adhesiveness of stored Hom Bai Toei milled rice were 27.05 and 2.90 N, respectively. In addition, it was found that stored Hom Bai Toei brown and milled rice had lower 2AP than the fresh ones (p<0.05). However, high hexanal content was noticed. Fresh and stored Hom Bai Toei brown and milled rice which was cooked with high water content had higher in moisture content, water uptake and elongation ratio than those with low water content (p<0.05). In order to produce ready-to-eat rice, this reseach was aimed (1) to optimize the soaking time, (2) to investigate the heating process time (F) and (3) to monitor the quality of the ready-to-eat rice product during storage. Firstly, Hom Bai Toei brown and milled rice were soaked in boiling water and monitored moisture content and degree of gelatinization every 2 min in order to find the optimum soaking time. The result showed that the optimum conditions for brown rice were 8, 10 and 12 min and milled rice were 6 and 8 min. The moisture content and degree of gelatinization of Hom Bai Toei brown and milled rice were in the ranges of 60.01-64.64% and 70.78-89.93%, respectively. Next step, the sterilization process of cooked Hom Bai Toei brown and milled rice was investigated. Rice was packed in a retort pouch 125 grams/bag, then sealed and sterilized in a retort at 118°C with pressure 23 pound/square inches. The heating process time of Hom Bai Toei brown rice was 26.30 min (F, Formula = 4.29 min), while heating process time of Hom Bai Toei milled rice was 23.30 min (F, Formula 4.08 min). The sensory evaluation 9-point Hedonic scale was monitored for Hom Bai Toei brown and milled rice that was packed in a retort pouch. The result showed that Hom Bai Toei brown rice in a retort pouch that was soaked for 10 min under boiling water and Hom Bai Toei milled rice in a retort pouch that was soaked for 6 min under boiling water had the highest score in texture and overall liking scores. The hardness and adhesiveness of cooked Hom Bai Toei brown rice were 54.83 and 2.62 N, respectively. While, the hardness and adhesiveness of cooked Hom Bai Toei milled rice were 26.88 and 2.89 N, respectively. Finally, Hom Bai Toei brown and milled rice in a retort pouch was stored under room temperature for 6 months. The changes in physical, chemical, physicochemical properties as well as sensory evaluation in each month were determined. It was found the retrogradation increased in all treatments during storage (p<0.05). It was considered as the increasing of enthalpy and hardness (p<0.05) and the decreasing of moisture content and adhesiveness (p<0.05). Texture and overall liking scores of Hom Bai Toei brown and milled rice in a retort pouch decreased during storage (p<0.05). Therefore Hom Bai Toei brown rice that was soaked for 10 min and Hom Bai Toei milled rice that was soaked for 6 min before packing in a retort pouch and sterilization had the highest in texture and overall liking scores (p<0.05).