Researches:

Article title: Long glucan chains reduce in vitro starch digestibility of freshly cooked and retrograded milled rice
Authors: Crisline MaeAlhambra, Maria Krishnade Guzman, Sushil Dhital, Aldrin P. Bonto, Erlinda I.Dizon, Katherine Ann C.Israel, Wilma A. Hurtada, Vito M. Butardo Jr., Nese Sreenivasulu
Publication title: Journal of Cereal Science 86, February 2019

Abstract:
Understanding the structural factors related to the starch digestibility of cooked milled rice grains is important in mitigating the impact of diet-related diseases. In this study, changes in starch structure of rice during in vitro digestion and retrogradation is reported for 8 varieties of indica milled rice with apparent amylose ranges from 3 to 34. Results showed that retrogradation is effective in decreasing starch hydrolysis rate (k), while addition of exogenous lipid had no significant effect. Moreover, reduction in digestibility after retrogradation was more effective in high amylose than low amylose or waxy rice. Structurally, strong negative correlations were found between k and starch fractions rich in long glucan chains such as long-chain amylose (LCAM) or intermediate-chain amylose (ICAM). Conversely, strong positive correlation was seen between k and short-chain amylopectin (SCAP). Decreased hydrolysis of LCAM and low levels of SCAP was observed in retrograded rice. This shows that LCAM becomes less susceptible to digestion which consequently results to increased hydrolysis of SCAP as the preferred substrate in rice.
Full text available upon request to the author/s.

Article title: Investigating glycemic potential of rice by unraveling compositional variations in mature grain and starch mobilization patterns during seed germination
Authors: Maria Krishna de Guzman, Sabiha Parween, Vito M. Butardo, Crisline Mae Alhambra, Roslen Anacleto, Christiane Seiler, Anthony R. Bird, Chung-Ping Chow & Nese Sreenivasulu
Publication title: Scientific Reports 7(1), July 2017

Abstract:
Rice lines with slower starch digestibility provide opportunities in mitigating the global rise in type II diabetes and related non-communicable diseases. However, screening for low glycemic index (GI) in rice breeding programs is not possible due to time and cost constraints. This study evaluated the feasibility of using in vitro cooked grain amylolysis, starch mobilization patterns during seed germination, and variation in starch structure and composition in the mature seed to differentiate patterns of starch digestibility. Mobilization patterns of total starch, resistant starch, amylose and amylopectin chains, and free sugars during seed germination revealed that the process is analogous to digestion in the human gastrointestinal tract. The combination of these biochemical markers can be used as an alternative measure to predict GI. Additionally, transcriptome analysis of stored mRNA transcripts in high and low GI lines detected differences in starch metabolism and confirmed the importance of seed storage pathways in influencing digestibility. Pathway analyses supported by metabolomics data revealed that resistant starch, cell wall non-starch polysaccharides and flavonoids potentially contribute to slower digestibility. These new insights can guide precision breeding programs to produce low GI rice with acceptable cooking quality to help mitigate the burden of diet-associated lifestyle diseases.
Full text link https://tinyurl.com/pcnzvma5

Article title: Systems Genetics Identifies a Novel Regulatory Domain of Amylose Synthesis
Authors: Vito M. Butardo Jr., Roslen Anacleto, Sabiha Parween, Irene Samson, Krishna de Guzman, Crisline Mae Alhambra, Gopal Misra, and Nese Sreenivasulu
Publication title: Plant Physiology 173(1):01248.2016, November 2016

Abstract:
A deeper understanding of the regulation of starch biosynthesis in rice endosperm is crucial in tailoring digestibility without sacrificing grain quality. In this study, significant association peaks on chromosomes 6 and 7 were identified through genome-wide association study (GWAS) of debranched starch structure from grains of a 320 indica rice diversity panel using genotyping data from the high-density rice array. A systems genetics approach that interrelates starch structure data from GWAS to functional pathways from a gene regulatory network identified known and novel genes with high correlation to the proportion of amylose and amylopectin. A novel SNP in the promoter region of Granule Bound Starch Synthase I (GBSS I) was identified along with seven other SNPs to form haplotypes that discriminate samples into different phenotypic ranges of amylose. A novel GWAS peak on chromosome 7 between LOC_Os07g11020 and LOC_Os07g11520 indexed by a non-synonymous SNP mutation on exon 5 of a bHLH transcription factor was found to elevate the proportion of amylose at the expense of reduced short-chain amylopectin. Linking starch structure with starch digestibility by determining the kinetics of cooked grain amylolysis of selected haplotypes revealed strong association of starch structure with estimated digestibility kinetics. Combining all results from grain quality genomics, systems genetics, and digestibility phenotyping, we propose novel target haplotypes for fine-tuning starch structure in rice through marker-assisted breeding that can be used to alter the digestibility of rice grain, thus offering rice consumers a new diet-based intervention to mitigate the impact of nutrition-related non-communicable diseases.
Full text link https://tinyurl.com/mvay73f3

Chapter title: Quantifying Grain Digestibility of Starch Fractions in Milled Rice: Methods and Protocols
Authors: Crisline Mae Alhambra, Sushil Dhital, Nese Sreenivasulu & Vito M. Butardo Jr.
Publication title: Methods in Molecular Biology, January 2019

Abstract:
Rice is one of the staple foods which serves as the major source of carbohydrate in the human diet. A typical milled rice grain is mainly composed of starch of up to 80–90%, with an average of 6–8% proteins and some trace amounts of dietary fiber. Although cooked white rice can elicit variable glycemic response, a portion of rice starch may evade digestion in the human small intestine. The digested portion of rice can be estimated and characterized in vitro based on starch digestion extent and rate (kinetics). The indigestible portion of starch can also be quantified. This chapter will present micro-scale methods to quantify rice starch digestion rate and extent based on the sugar fractions released after treating the samples with digestive enzymes.
Full text available upon request to the author/s.

Article title: Development and Validation of Amylolysis Method to Assess Digestibility of Rice Grains
Authors: Vito M. Butardo Jr., Krishna de Guzman, Crisline Mae Alhambra, Asgar Faranahky, Laura, Pallas, Christopher Blanchard and Nese Sreenivasulu
Conference title: 2017 AIFST Food Science Summer SchoolAt: Western Sydney University Hawkesbury Campus

Abstract:
Rice is an important energy source for more than half of the world’s population. Understanding the digestibility of rice grains is crucial in mitigating the impact of hunger and overnutrition. In this paper, we summarise more than one decade of research efforts on rice digestibility to address the global prevalence of malnutrition. In the past, we screened for grain digestibility using amylose content as proxy measure. Digestibility was then verified using an in vitro starch hydrolysis method. This strategy proved to be effective in identifying starch mutants with extremely reduced digestibility. However, this was accomplished at the expense of reduced grain quality and consumer acceptance. Consequently, recent phenotypic screening focused on characterising rice grains from diversity panels with subtle allelic variations. Using this diversity screening approach, we identified some rice accessions that can be used as parental sources to tailor the digestibility of rice grains by marker-assisted breeding. After initial screening, selected rice lines representing glutinous to very high amylose varieties were subjected to cooked grain amylolysis to determine in vitro digestibility kinetics. The role of endogenous and exogenous factors that can alter digestibility kinetics were also determined. Lastly, we present our recent efforts in developing an accurate and robust phenotyping method to quantify rice grain digestibility focusing on Australian commercially-released rice varieties. A quick and low-cost phenotyping method to characterize rice digestibility is important in screening thousands of samples within the Australian rice breeding program each year. We believe that this current strategy is better in improving the nutritional quality of rice grains without sacrificing other grain quality traits essential in maintaining consumer acceptance.
Full text link https://tinyurl.com/4swdhke3