Ismail, Muhammad Heikal
(2019)
Investigating the effect of pre-treatment on the drying kinetics and quality traits of rice noodles.
PhD thesis, University of Nottingham.
Abstract
Rice noodle has long been a very common food to most East Asians. Moreover, the overwhelming trend towards gluten-free food which introduces positive health beneficial effects has currently promoted rice noodle throughout the world. In spite of that, fresh rice noodle is truly perishable and prone to degradation within several days. Therefore, there is an urgent need to produce the good preservation of high quality fresh rice noodle of a good textural and cooking quality with an adequate shelf life. Therefore, the shelf life of rice noodle will be prolonged by the means of drying. Unfortunately, there is a lack of research on the processing aspects to produce better quality of dried rice noodle.
Indeed, this research focused on three key areas which include pre-treatment, drying processes, and quality parameter. Pre-treatment was performed by fully rinsing the rice noodle in distilled water to represent the low-fat noodle defined as non-oil coated sample in the study as compared to the original noodle. These two types of rice noodles were then subjected to three drying methods which were hot air drying, heat pump drying and freeze drying. The dried noodles were then subjected to the quality analysis including texture, colour, microstructures, fat content, starch gelatinization, rehydration ratio, and sensory evaluation. In addition to that, the transparency phenomenon was further described through physical inspection, colour analysis, and starch gelatinization.
The pre-treatment slightly reduced the drying time and increased the effective diffusivity. The effective diffusivities resulted for the first falling rate of non-oil coated and original rice noodle subjected to hot air drying at 30 ˚C are 1.60 x 10-11 m2/s, and 1.25 x 10-11 m2/s, respectively. The effective diffusivities obtained for the second falling rate of the respective non-oil coated and original rice noodle at 30 ˚C are 2.20 x 10-11 m2/s, and 1.71 x 10-11 m2/s. The effective diffusivities resulted for the first falling rate of original rice noodle at 60 ˚C and 90 ˚C are 6.35 x 10-11 m2/s and 1.26 x 10-10 m2/s respectively. The effective diffusivities obtained for the second falling rate of original rice noodle at 60 ˚C and 90 ˚C are 7.59 x 10-11 m2/s and 1.18 x 10-10 m2/s respectively.
This is in agreement to the effective diffusivity obtained in the heat pump drying of rice noodles. The effective diffusivities resulted for the first falling rate of non-oil coated and original rice noodle subjected to heat pump drying at 38 ˚C are 7.75 x 10-11 m2/s, and 5.59 x 10-11 m2/s respectively. The effective diffusivities obtained for the second falling rate at 38 ˚C for non-oil coated and original rice noodle at 38 ˚C were respectively at 2.431 x 10-11 m2/s. The effective diffusivities obtained for the first falling rate period of respective non-oil coated and original noodle are 1.14 x 10-10 m2/s, and 1.05 x 10-10 m2/s respectively. The effective diffusivities obtained for the second falling rate at 50 ˚C give straight lines for the non-oil coated and original rice noodle were respectively at 9.575 x 10-11 m2/s and 8.78x 10-11 m2/s.
Most quality attributes of rice noodle subjected to hot air drying and heat pump drying were declining which eventually led to the best quality preservation by freeze drying. In conjunction to that, transparency phenomenon can be clearly described through several quality analysis of rice noodle subjected to hot air and heat pump drying. Apparently, transparency phenomenon in rice noodle due to hot air and heat pump drying was deduced to have a more stable shelf life due to low microbial growth. After analysing the overall quality performance, heat pump drying at 38 ˚C is deemed as a convenient drying method in producing comparatively good quality attributes of dried rice noodle.
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