Exploring Fermented Rice-Based Foods: A Review of Nutritional Enhancement, Microbial Analysis, and Global Health Implications

Abstract

Fermentation is an ancient food practice utilized to enhance food flavor, preservation, and nutritional value. This review delves into the topic of fermented rice-based foods, particularly focusing on their nutritional attributes and potential health benefits. With white rice being a staple for major global staple food, nutrient deficiencies due to lack of diet diversity are of concern. Strategies such as fortification and enrichment have emerged to combat these deficiencies, yet cultural preferences pose challenges. Fermentation offers a promising avenue to augment rice’s nutritional profile by removing antinutrient factors and increasing antioxidants. Microbial, biochemical, and sensory evaluations are utilized to study these fermented rice foods, highlighting the potential of fermentation in enhancing rice’s nutritional quality. Furthermore, fortified fermented rice products along with nutrition education have the potential to address global nutritional disparities. Rice fermentation emerges as a potent tool in enhancing nutritional gaps and global health.

1. Introduction

Fermentation is a food practice that has been used for thousands of years to preserve and enhance the flavor of food and, in some instances, its nutritional value. The process of fermentation is characterized by the activity of microorganisms breaking down substrates, such as carbohydrates, resulting in changes to a food product through the production of organic acids and alcohols. As the fermentative process results in significant physicochemical changes to the food, many parameters can be studied to determine the effectiveness and extent of fermentation.

This fermentative process has been applied to various foods, including grains. Grain-based fermentation extends to fermented rice products, which are staple foods in many parts of the world, particularly in South Asia. Extensive research has shed light on the nutritional value, health benefits, microbial diversity, and sensory properties of rice fermentation. Considering the vast array of diverse fermented rice-based dishes, some have not been explored, such as overnight fermented rice, originating in South Asia, where rice covered in water is fermented over 12 hours. This review aims to provide a comprehensive understanding of fermented rice-based foods, their potential health benefits, and their ability to address global nutritional concerns.

2. Global rice consumption and nutrient concerns

Rice is a staple food for over half of the global population, providing more than 20% of the world’s kilocalories [1]. According to a recent statistical report 520.4 million metric tons of rice was consumed in the 2022/2023 crop year [2]. It grows in over 100 countries, with 10 of the highest rice-producing countries in Asia [3]. After harvest and processing, rice is typically categorized as either white or brown, with white rice having the bran removed, resulting in the loss of certain nutrients and phytochemicals [1]. During the bran removal or polishing process, 85% of the fat, 15% of protein, 75% of phosphorus, 90% of calcium, and 70% of B vitamins (B1, B2, and B3) are lost [4]. While white rice remains a significant source of carbohydrates and trace micronutrients, the nutrient losses during polishing are significant. Furthermore, with white rice being a significant source of energy for billions of people, a lack of diet diversity contributes to micronutrient deficiencies, including iron, vitamin A, and folate, which can lead to iron deficiency anemia [5]. This is further exacerbated in developing regions, like South Asia. Despite economic growth, and health care improvement, micronutrient deficiencies of iodine, iron, vitamin A, and zinc are still high in South Asia [6].

One method to address these deficiencies would be to increase the consumption of unpolished rice in micronutrient-deficient populations. However, cultural factors and the influence of regional preferences pose a challenge to the acceptability of nutritionally beneficial rice products. Some studies on consumer preferences shed light on methods to overcome these obstacles in broader populations. A study conducted in the city of Chennai in Tamil Nadu, India compared polished rice varieties and consumer acceptance. It found that participants strongly preferred the polished rice samples in terms of color, appearance, texture, taste, and overall quality. In contrast, unmilled brown rice received lower preference ratings. However, upon learning of the nutritional benefits of unmilled rice, 93% of the participants expressed a willingness to switch to unmilled rice varieties [7]. In another study conducted in Nepal, participants also expressed interest in incorporating brown rice into their diets upon learning of the health benefits [8]. These studies showed that nutrition education and knowledge played a key role. This illustrates that nutrition education could be a potential solution to address the hesitation in the adoption of healthier rice products.

In response to global nutritional concerns, fortification, and enrichment have emerged as strategies to enhance the nutrient content of food products. Fortification and enrichment are food processing methods in which micronutrients, such as iron and B vitamins, are added to foods to increase their nutrient value [9]. Enrichment involves the replacement of the specific micronutrients lost in the milling process, and fortification includes the addition of any beneficial micronutrient. Globally, 140 countries have regulations for fortification programs, with iodized salt and fortified grain among the most common [10]. Rice fortification could be one way to potentially address micronutrient deficiencies. As a major global food source, rice can serve as an optimal vessel for fortification to address micronutrient deficiencies at a population level [5]. A study was conducted in Bangladesh to address anemia and zinc deficiency among women of reproductive age. The researchers provided participants with fortified rice containing added Vitamin A, Vitamin B1, Vitamin B12, folic acid, iron, and zinc. This resulted in a decrease in anemia prevalence by 4.8% [11]. Furthermore, voluntary fortification also emerges. Some private companies, such as Olam in Ghana, have elected to add iron, zinc, and B-complex vitamins to their long-grain rice, providing consumers with 15% of their recommended dietary allowance [10].

3. Benefits of rice fermentation

Fermentation as a food practice has been adopted by various food cultures across the world. During fermentation, the fermentative microorganisms impart several changes to the food products, including extending preservation time, enhancing flavor profiles, and increasing nutritional values. Rice-based fermented foods are often the result of endogenous microorganisms. The primary fermentative organisms in rice-based fermented foods are lactic acid bacteria (LAB), lactobacilli, bifidobacteria, yeasts, and molds [12]. LAB are known to produce antioxidants in fermented foods, including active phenolic metabolites, chlorogenic acid, and sulforaphane [13]. Previous studies have also identified several LAB strains as probiotic candidates, such as Lactobacillus fermentum KKL1 [14, 15]. This combination of antioxidants and probiotics in rice-based LAB fermented foods showcase its health benefits.

Another benefit of fermentation is its ability to enhance and improve the nutritional value of foods. This is achieved through the elimination of anti-nutrient factors. Some cereals and legumes contain trypsin inhibitors and phytates, which impede protein digestion and mineral release, respectively [16]. Fermentation of these cereals and legumes results in the activation of endogenous enzymes, which disrupt the function of these inhibitors and phytates [16]. The removal of these anti-nutrient factors makes macronutrients more accessible. LAB fermented foods have also been shown to increase the bioavailability of certain minerals from plant sources, including calcium, zinc, and iron [17, 18]. Fermentation of germinated brown rice has also been shown to increase its bioactive compound profiles and anti-inflammatory properties [19]. One specific rice-based fermented food, originating from Tamil Nadu, India is fermented cooked rice water or “pazhaya sadham” in Tamil [20]. This fermented rice dish offers not only nutritional benefits but also potential health applications. A study has shown that fermented cooked rice water effectively inhibits the proliferation of hepatocellular carcinoma cells in an in vitro assay, making it a potential source of natural therapeutic agents against cancer [20].

4. Evaluation of fermented rice foods

The process of fermentation is characterized by several biochemical and molecular changes through microorganism activities. Various approaches are employed to explore the microbial, biochemical, and sensory profiles of these foods.

4.1 Microbial analysis

Microbial analysis is a fundamental aspect of fermentation research as the fermentative microorganisms, including LAB, yeasts, and molds are known to fluctuate during the process [12]. The microbial succession influences the development and outcome of the fermentation process over time. In the study of the fermentation of Haria, an east Indian rice beer, molds and yeasts peaked on the 2nd day of fermentation while LAB and Bifidobacterium increased simultaneously [21]. The enumeration of these microorganisms was conducted on specialized media with figures outlining peaks of their activity [21]. A study on idli fermentation, an Indian fermented food made from rice and black gram, used advanced techniques, such as 16S rRNA amplicon sequencing, denaturing gradient gel electrophoresis, and quantitative PCR to explore the microbial dynamics of the process [22]. These analyses provided insights into the diversity and succession of microbial populations throughout the fermentation process.

4.2 Biochemical analysis

Biochemical analysis is another important component to understanding rice fermentation. During the process, fermentative microbes enzymatically degrade macromolecules in food substrates, producing amino acids, sugars, and fatty acids which participate in further biological and chemical reactions [23]. The fermentative process in rice yields various compounds, including, organic acids, phenolics, saccharides, antioxidants, and amino acids. Quantification methods such as Gas chromatography-mass spectrometry (GC-MS) allow for the assessment of saccharides and their derivatives [21]. Organic acid extracts from fermented rice have been analyzed by High-Performance Liquid Chromatography (HPLC) [24]. These specialized methods and tools enable the identification and quantification of minute biochemical changes in fermented rice foods.

4.3 Sensory evaluation

Sensory evaluation plays a key role in the development and improvement of rice-based fermented foods. By systematically assessing taste, aroma, and texture, it is possible to measure product quality and consumer acceptance [25]. A study by Zhang et al. [26] explored the effects of solid-state fermentation on the sensory characteristics of brown rice. The study found that fermentation significantly improved the overall sensory score of brown rice, raising it from 59.82 (control group) to 74.22 (highest score) (p < 0.05) [26]. This improvement was attributed to the production of unique flavors through the release of volatile compounds during fermentation, as well as the increase in free amino acids, such as glutamic and aspartic acids. Additionally, the hydrolysis of the rice softened the texture and enhanced the appearance, taste, and overall sensory quality. A study by Chelliah et al. [27] examined the impact of adding curry leaves to idli batter and how this affected sensory qualities including appearance, texture, mouthfeel, flavor, aftertaste, and overall acceptability. The results showed a clear preference for idlis made with curry leaves, demonstrating higher sensory scores across all evaluated attributes compared to control idlis. This study not only confirms the acceptance of fermented rice-based products, but specifically shows an increased interest in the aspect of enrichment.

5. Conclusion

The prevalence of global rice consumption can often lead to micronutrient deficiencies in vulnerable populations, particularly in Asia. While whole grain and fortified rice products can provide a method to address these deficiencies, cultural and regional factors pose a barrier. Rice fermentation also showcases the ability of microorganisms, including (LAB) to alter the nutrient composition of rice. Through the elimination of antinutrient factors and the increase of antioxidants, the fermentative process can yield nutritional benefits. Through nutrition education and the development of novel fortified fermented rice foods, micronutrient deficiencies may be addressed. Rice fermentation has the potential to bridge nutritional gaps and promote health.

Acknowledgments

Authors would like to acknowledge funding support from Graduate Student Research Assistance Award from Department of Nutrition, Food Science, and Packaging, San José State University (San Jose, CA 95192, USA).

Thanks

Thank you to the faculty at the Department of Nutrition, Food Science, and Packaging, San José State University.