Combined Insights from Leachate Structure and Microstructure Characteristics for Eating Quality of Convenience Rice Processed by Super-Heated and Pressurized Steam Technologies

doi:10.1016/j.rsci.2024.02.006

Abstract

Abstract:

Convenience rice has become widely popular due to its easy availability for cooking. This study investigated the starch structure and composition of leachate and the microstructure of reheated convenience rice using novel processing technologies: super-heated steaming (SHS), auto-electric cooking (AEC), and pressurized-steam cooking (PSC). Additionally, the effect of two different target water contents (58% and 63%) was also evaluated. The PSC_63% sample had the highest total solids and amylopectin amount in the leachate. The amylopectin amount in the leachate differed significantly based on the targeted water content. Morphological characterization revealed that the swelling of starch and the coated layer on the surface of rice grains were most pronounced in the PSC_63% sample due to the pressure processing. The textural hardness of the AEC_58% sample was much higher than that of the other samples. The PSC_63% sample had the highest textural adhesiveness value, which can be attributed to the highest amylopectin amount in the leachate. Sensory characterization showed that the PSC_63% sample had the highest glossiness, whiteness, moistness, and overall acceptability. The principal component analysis score plots presented substantial differences in the leachate and textural and sensory characteristics of reheated convenience rice among the different processing technologies.

Key words: reheated convenience rice, starch structure, leachate, multi-scale structure, eating quality, processing technology

Mingyo Ha, Hyo-Young Jeong, Ju Hun Lee, Hyun-Jung Chung. Combined Insights from Leachate Structure and Microstructure Characteristics for Eating Quality of Convenience Rice Processed by Super-Heated and Pressurized Steam Technologies[J]. Rice Science, 2024, 31(4): 475-488.

Figures/Tables 8

Table 1. Compositions of leachate obtained from convenience rice using different processing technologies.

Reheated convenience rice	Total solid content (mg/g)	Protein content (%)	Total starch content (%)	Amylose content (%)	Amylopectin amount (mg/g)
SHS_58%	15.0 ± 1.9 c	4.9 ± 0.3 b	78.2 ± 0.3 c	17.0 ± 0.5 b	9.2 ± 0.0 e
SHS_63%	20.2 ± 0.5 b	5.1 ± 0.2 ab	78.9 ± 0.4 c	17.4 ± 0.5 ab	12.4 ± 0.1 d
AEC_58%	24.2 ± 0.9 ab	5.3 ± 0.2 a	80.6 ± 0.6 b	18.4 ± 0.2 a	15.1 ± 0.1 c
AEC_63%	27.7 ± 3.7 a	5.4 ± 0.2 a	81.5 ± 0.2 ab	18.6 ± 0.3 a	17.2 ± 0.0 b
PSC_63%	28.4 ± 1.1 a	5.4 ± 0.1 a	81.8 ± 1.4 a	18.5 ± 0.6 a	18.0 ± 0.3 a

Table 2. Amylopectin branch chain length distribution of leachate obtained from convenience rice using different processing technologies.

Reheated convenience rice	Average chain length (DP)	Amylopectin chain length distribution (%)
Reheated convenience rice	Average chain length (DP)	DP 6‒12 (A chain)	DP 13‒24 (B1 chain)	DP 25‒36 (B2 chain)	DP ≥ 37 (B3+ chain)
SHS_58%	19.3 ± 0.0 b	30.3 ± 0.0 b	48.8 ± 0.3 a	11.0 ± 0.0 a	9.9 ± 0.3 b
SHS_63%	19.4 ± 0.1 ab	30.4 ± 0.2 b	48.4 ± 0.1 b	11.0 ± 0.0 a	10.3 ± 0.1 ab
AEC_58%	19.4 ± 0.0 ab	30.3 ± 0.2 b	48.2 ± 0.1 b	11.1 ± 0.1 a	10.4 ± 0.1 a
AEC_63%	19.4 ± 0.0 ab	30.5 ± 0.2 ab	48.2 ± 0.1 b	11.0 ± 0.0 a	10.3 ± 0.1 ab
PSC_63%	19.5 ± 0.1 a	30.8 ± 0.4 a	48.5 ± 0.3 ab	10.4 ± 0.3 b	10.4 ± 0.3 a

Table 3. Textural properties of convenience rice using different processing technologies.

Reheated convenience rice	Hardness (g)	Adhesiveness (g∙s)	Springiness	Cohesiveness	Chewiness (g)
SHS_58%	2 705.0 ± 10.1 c	9.3 ± 0.5 e	0.819 ± 0.015 b	0.624 ± 0.011 b	1 272.6 ± 15.2 c
SHS_63%	2 546.5 ± 37.0 d	10.5 ± 0.6 d	0.832 ± 0.022 b	0.624 ± 0.008 b	1 178.8 ± 22.0 d
AEC_58%	3 242.2 ± 13.3 a	13.0 ± 0.5 c	0.874 ± 0.008 a	0.659 ± 0.005 a	1 768.1 ± 25.6 a
AEC_63%	2 160.0 ± 19.3 e	16.9 ± 0.7 b	0.837 ± 0.031 b	0.613 ± 0.012 b	1 103.9 ± 9.0 e
PSC_63%	2 817.6 ± 39.3 b	19.5 ± 0.4 a	0.767 ± 0.028 c	0.598 ± 0.009 c	1 438.1 ± 38.7 b

Table 4. Sensory characteristics of reheated convenience rice using different processing technologies..

Reheated convenience rice	Glossiness	Whiteness	Roasted flavor	Hardness	Stickiness	Moistness	Overall acceptability
SHS_58%	4.6 ± 0.5 d	6.8 ± 0.4 a	4.7 ± 0.5 b	6.3 ± 0.5 b	3.4 ± 0.5 c	3.1 ± 0.3 d	5.3 ± 0.5 b
SHS_63%	5.3 ± 0.5 c	6.6 ± 0.5 a	4.4 ± 0.5 b	5.6 ± 0.5 c	5.3 ± 0.5 b	4.6 ± 0.5 c	4.4 ± 0.5 c
AEC_58%	5.4 ± 0.5 c	5.6 ± 0.5 b	6.6 ± 0.5 a	7.8 ± 0.9 a	5.7 ± 0.9 b	4.8 ± 0.4 c	5.9 ± 0.4 b
AEC_63%	6.5 ± 0.5 b	5.3 ± 0.5 b	6.5 ± 0.5 a	5.5 ± 0.6 c	6.5 ± 0.5 a	5.5 ± 0.5 b	5.5 ± 0.5 b
PSC_63%	8.5 ± 0.5 a	4.3 ± 0.9 c	4.3 ± 0.5 b	6.9 ± 0.9 b	5.4 ± 0.5 b	6.7 ± 0.8 a	6.8 ± 0.9 a

Fig. 1. Scanning electron microscopy images of outer (A1‒E1) and inner (A2‒E2) cross-section, and surface (A3‒E3) of reheated convenience rice using different processing technologies (500× magnification). A1‒A3, Super-heated steaming with 58% water content (SHS_58%); B1‒B3, Super-heated steaming with 63% water content (SHS_63%); C1‒C3, Auto-electric cooking with 58% water content (AEC_58%); D1‒D3, Auto-electric cooking with 63% water content (AEC_63%); E1‒E3, Pressurized-steam cooking with 63% water content (PSC_63%). The red arrows in E2 indicate longitudinal chunks, and white lines in A1‒E1 represent the thickness of coated layer.

Fig. 2. Confocal laser scanning microscopy images of outer (A1‒E1) and inner (A2‒E2) regions of reheated convenience rice using different processing technologies (200× magnification). A1 and A2, Super-heated steaming with 58% water content (SHS_58%); B1 and B2, Super-heated steaming with 63% water content (SHS_63%); C1 and C2, Auto-electric cooking with 58% water content (AEC_58%); D1 and D2, Auto-electric cooking with 63% water content (AEC_63%); E1 and E2, Pressurized-steam cooking with 63% water content (PSC_63%). The green and red colors in images indicate starch and protein in the reheated convenience rice, respectively. White arrows in A1, A2, B1, and B2 indicate polygonal starch granules.

Fig. 3. Score (A) and loading (B) plots for principal component analysis (PCA) derived from leachate compositions and textural and sensory characteristics of reheated convenience rice using different processing technologies. SHS, Super-heated steaming; AEC, Auto-electric cooking; PSC, Pressurized-steam cooking; TA, Texture analysis; SE, Sensory evaluation; ACL, Average chain length; DP, Degree of polymerization. 58% and 63% are two target water contents.

Fig. 4. Pearson correlation coefficients for relationship between compositions of leachate, texture properties, and sensory characteristics of reheated convenience rice using different processing technologies. TA, Texture analysis; SE, Sensory evaluation; ACL, Average chain length; DP, Degree of polymerization. *, **, and *** mean that the correlations are significant at P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively.

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