Effect of Parboiling on the Physicochemical and Phytochemicals Characteristics of Traditional Rice Cultivars

Rice (Oryza sativa L.) is a significant staple food for above half of the world’s population and was more produced and consumed in the Asian countries. The cultivation and consumption of traditional grains is commonly distributed worldwide. At present, the traditional rice varieties are differentiated based on the colour intensity as red, black, purple and brown rice (Singh et al., 2019).
       
Traditional red rice is an unpolished grain coated with germ, bran and endosperm. These grains are a store house of secondary metabolites and nutraceutical compounds like polyphenols, phenolic acids, tocopherols, tocotrienols, flavonoids, terpenoids, anthocyanins, proanthocyanidins and g-oryzanol. The compounds are contributed to various health benefits as boosting of immunity, increasing memory power in children and fighting against cancer cells (Qayyum et al., 2020). The traditional rice grains are generally cooked and consumed as a whole. Parboiled rice undergoes gelatinization and retrogradation and it change the structural features of rice starch, converting crystalline to amorphous form, producing very compact and translucent endosperm (Toutounji et al,. 2019).
       
Though considering the nutritional aspects of traditional rice varieties in the grain, the consumers are still restrained and are underutilized. Thus, keeping in view of above facts the present research work was undertaken with the objective to analyze physicochemical characteristics and phytochemicals content in traditional red and white rice varieties and their retention of the nutrients in raw and parboiled rice varieties in Tamil Nadu, India.
 

The experiments were conducted in the Department of Food Science and Nutrition, Community Science College and Research Institute, Madurai during month of Feburary, 2022. The traditional red rice cultivars viz., mapillai samba and karungkuruvai in the form of paddy were procured from Tamil Nadu Rice Research Station (TRRI), Aduthurai and from organic rice farmer, Srivilliputhur. The traditional white rice cultivars viz., IR 20 and improved white ponni were obtained from Agricultural College and Research Institute, Madurai.
 
Analytical methods
 
Physicochemical and phytochemical analysis of selected rice cultivars
 
Ten rice kernels (undamaged and sound) of selected rice cultivars were analyzed for length (L) and breadth (B) using vernier caliper and were expressed in mm (Odenigbo et al., 2014). Thousand grains from all samples were weighed by using an electronic weighing balance to determine thousand grains weight. Bulk density (BD) and porosity (P) of the rice samples were analyzed as per the procedure followed by Bhattacharya and Sowbhagya (1971), expressed as g/cc and percentage (%).
       
The cooking time (CT) for the selected rice samples were made as per the procedure followed by Simpson et al., (1965). Solid loss (SL), kernel elongation ratio (KER), water absorption index (WAI) and water solubility index (WSI) were determined by Simpson et al., (1965).The amylose and amylopectin were analysed by AOAC (2000).
       
Total phenols present in the extracts of selected traditional and white rice cultivars was done by Folin–Ciocalteau assay with a gallic acid standard (Singleton and Rossi, 1965). Total flavonoids present in rice sample extract of selected cultivars were determined by using aluminum chloride (Singh et al., 2019). The existence of the total anthocyanins was estimated as per the procedure followed by Shen et al., (2012) by pH differential method. The 2,2-diphenyl-1-picrylhydrazyl-radical scavenging activity (DPPH), ferric reducing antioxidant power (FRAP) and radical cation ABTS scavenging activity were analysed by using the method Lim et al., (2007). The data obtained from the study were analysed by SPSS software of 2017 version of one-way analysis of variance (Snedecor and Cochran, 2004). Principal component analysis (PCA) was performed using XLSTAT software.
 

Physicochemical characteristics of raw and parboiled rice cultivars
 
The physical properties viz., L, B, 1000 grain weight, BD and P were assessed and presented in (Table 1). The length and breadth ranged from 5.02±0.06 to 5.92±0.13mm and 1.00±0.06 to 2.28±0.07 mm in selected rice varieties. The findings were comparable to the results obtained by Muthamilarasan et al., 2016 who analyzed the length, breadth and L/B ratios of 5.24 mm, 1.85 mm and 2.83 in navara, a traditional rice variety. The thousand grain weight of the rice cultivars ranged from 14.3 to 26.7 g. The bulk density ranged from 0.36±0.01 to 0.70±0.08 g/cc in selected rice cultivars. Sareepuang et al., (2018) reported that the traditional rice varieties have higher 1000 grain weight, bulk density and porosity when compared to the white rice varieties. The maximum and minimum porosity was observed in raw-unpolished IR 20 of 58.32±0.74% and 49.22±0.45% in raw-polished mapillai samba. Lee et al., (2011) stated that the porosity of basmati and non basmati rice varieties ranged from 40 to 54% respectively.


       
The cooking characteristics viz., CT, KER, SL, WAI, WSI, amylose and amylopectin are presented in (Table 2). The traditional rice cultivars required more time for cooking then white rice cultivars. Furthermore, this is consistent with the study conducted by Pushpama and Reddy (2017). The KER ranged from 1.02±0.02 to 2.32±0.03% for the selected rice cultivars. The solid loss values varied from 3.91 to 4.97% in selected rice cultivars. The highest WAI of 2.44±0.01g/g was noted in raw-unpolished mapillai samba. Odenigbo et al., 2014 reported that this difference in WAI is due to the disparity between the hydrogen and hydroxyl groups in forming a bond between the starch structures. Among the traditional rice cultivars, raw-unpolished mapillai samba showed highest WSI of 6.58±0.10g/g and with a lowest of 4.82±0.08g/g in parboiled-polished karungkuruvai. In case of white rice cultivars, the highest WSI was noted in raw-unpolished IR 20 of 5.59±0.16 g/g  and least of 5.30±0.03g/g in parboiled-polished improved white ponni. The amylose content of traditional rice cultivars ranged from 23.4 to 28.9% and white rice cultivars ranged from 22.0 to 24.9% respectively. The amylopectin content ranged between 71.3 and 78.0% for the selected rice cultivars.


 
Phytochemical constituents in raw and parboiled rice cultivars
 
The phytochemical constituents were analyzed and depicted in (Table 3). The highest TPC was noticed in raw-unpolished mapillai samba of 43.13±0.78 mgGAE/100 g. Shen et al., (2012) stated that among 492 rice accessions, TPC ranged from 108.1 to 1244.9mgGAE/100 g. The maximum and minimum TFC was observed in raw-unpolished mapillai samba of 7.20±0.68 mgQE/100 g and 0.94±0.03 mgQE/100 g in parboiled-polished improved white ponni. The highest TAC was noted in parboiled-unpolished karungkuruvai of 54.22±0.03 mgcy-3glc/100 g. Ghasemzadeh et al., (2015) analyzed and reported the mean flavonoid contents of red, black and white rice of 137.3, 125.7 and 194.2 mgRE/100 g.


       
The maximum DPPH activity was observed in raw-unpolished mapillai samba of 77.3±0.55% and minimum in parboiled-polished improved white ponni 11.9±0.30%. The FRAP activity ranged between 18.5±0.37 and 47.2±0.25%. The highest value of radical cation ABTS scavenging activity was noted in raw-unpolished mapillai samba of 40.2±0.05% and lowest in parboiled-polished improved white ponni of 15.2±0.16%. There was a significant difference in all the treatments of selected rice cultivars. Lee et al., (2011) investigated 582 rice cultivars viz., pigmented and non pigmented rice cultivars and stated that pigmented rice cultivars (red and blackish purple rice) had highest antioxidant activity then non pigmented rice cultivars. 
 
Multivariate analysis
 
The principal components analysis (PCA) was used in the experiment to minimize the reduction of research data while keeping the maximum number of variables in the study. (Table 4) shows the ‘Eigen’ value, as well as the variability percent and cumulative per cent. The factor loading computed for the first four components (PCs) are presented in (Table 5). In the analysis of selected rice cultivars, the first four principal components (PC1, PC2, PC3 and PC4) accounted for 94.52% of the variance, while PC1 for 66.03%, PC2 for 18.05%, PC3 for 6.42% and PC4 for 4.02% respectively. The Kaiser-Meyer-Olkin (KMO) measure of sampling adequacy is 0.689.        



              


       
The data from the loading matrix presented in (Table 5) revealed that PC1=66.03% of the variability was positively correlated with variables such as L, B, 1000 g wt, CT, WAI, TPC, TFC, TAC, DPPH, FRAP and ABTS, whereas WSI was negatively correlated with BD (Fig 1), which determines physicochemical characteristics of traditional and white rice cultivars. The second component, had positive correlation with amylopectin (PC2=18.05%). The third component (PC3=6.42%) had positive correlation with CT and a negative correlation with the WSI. The fourth component (PC4=4.02%) had positive correlation with CT but a negative correlation with TFC.


       
On the left side of PC2, RUV₃, PUV₃, RPV₃, RUV₄ and PUV₄ treatments were linked to SL, KER, BD, P and amylopectin as shown in (Fig 1). RUV₁, RPV₁, PUV₁, PPV₁, RUV₂, PUV₂, RPV₂, PPV₂, RUV₂, PUV₂, RPV₂, PPV₂ are located on the right side of PC1 related to L, B, 1000 grain weight, amylose, CT, WSI, WAI, TPC, TFC, TAC, DPPH, FRAP and ABTS.
 

In the midst of different treatments, it was perceived that parboiled-unpolished mapillai samba variety showed highest length, breadth and thousand grains weight followed by other rice cultivars. The highest value of bulk density and porosity were noticed in raw-unpolished IR 20 variety. The highest KER and solid loss were noted in parboiled-unpolished improved white ponni and IR 20 rice cultivars. The WAI and WSI were higher in raw-unpolished mapillai samba variety. The amylose content was higher for parboiled-polished karungkuruvai and improved white ponni rice cultivars .
       
The phytochemical contents and antioxidant activities were higher for the traditional red rice cultivars when compared to white rice cultivars. The correlation between physicochemical characteristics and phytochemicals had common or closely related pathways which were revealed by factor loading in PC1 and PC2, as well as the results of Pearson correlation analysis, demonstrating the reliability of the current experimental system. Hence, the study concludes that the variation in physicochemical characteristics maybe due to the varietal differences in selection of rice cultivars. The indigenous rice varieties are known to have potential in developing nutraceutical and functional foods. Utilization of these indigenous rice varieties in the form of value-added products by using traditional fermentation technique is likely to improve the gut microbiota and short chain fatty acids which in turn improve the consumption significantly at higher rates. As a result, there is a need to promote these rice varieties through improved production and processing, so that the individual can consume phytochemical-rich foods and improve their nutrition.
 

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