Strategies for Enhancing Functional Properties of Rice in Taiwan

Strategies for Enhancing Functional Properties of Rice in Taiwan

Published: 2022.08.18
Accepted: 2022.08.11
9
Researcher
Agricultural Policy Research Center, Agricultural Technology Research Institute, Taipei, Taiwan

ABSTRACT

In most countries, rice (Oryza Sativa L.) is one of the main dietary components of people and the most critical crop in Taiwan. Several factors, such as nutritional value and easy accessibility, are crucial for increasing rice consumption in people's daily diet. Therefore, it is necessary to enhance the functional values and health benefits of rice through processing techniques to attract consumers’ willingness to shop. Related studies show that genetic engineering techniques can enhance rice nutrient value during breeding. Grains harvested at different stages of maturity can increase the content of bioactive compounds, including dietary fiber, phenolics, and flavonoids. The functional compounds of rice are produced through fermentation, germination, or enzymatic transformation. Moreover, processing or cooking methods can modify the physical and nutritional properties via the micritization of rice. Because of the potential impacts on human health, rice products are attracting more attention from consumers, scientists, and health food businesses.

Keywords: Oryza Sativa L., rice, nutritional values, functional compounds, processing, milling

INTRODUCTION

Rice plants have strong environmental adaptability that can be grown in an extensive range of climatic and soil conditions. However, rice's nutritional values and bioactive compounds vary with different cultivars, soil fertility, season, application of fertilizers, and other environmental conditions. The biologically active phytochemicals in rice can not only provide essential nutrition to humans but also can prevent some chronic human diseases. Therefore, these compounds attract the food and medical industry to use them in their products.

In 2020, there were about 513.7 million tons of milled rice produced worldwide. Rice is a vital crop source of high-energy or high-calorie foods with a high nutritional value (OECD/FAO, 2021). The grain of rice constitutes water 14%, starch 75–80%, and protein about 7% with a full complement of amino acids. The protein in rice is dominated by alkali-soluble glutelin, which accounts for more than 80%, and lysine concentration (4%) among the protein is relatively higher and highly digestible with a high biological value (74 %) and a protein efficiency ratio. The most critical content of rice is carbohydrates, including the primary source of calorie-starch and dietary fiber (Juliano, 1993).

Some extra and highly concentrated nutritional components in brown rice or germ rice are typically presented in bran, germ fraction, and endosperm. The above nutrients with small quantities have performed different biological activities. In addition to dietary fiber that can help gastrointestinal motility and lower blood cholesterol, the nutritional components also contain the essential nutrients of vitamins B1 and B2, which can metabolize energy and maintain the health of the nervous system, heart, stomach, oral cavity, skin, etc. The bran layer is an abundant source of some minerals that supply magnesium, phosphorus, iron, and zinc. Besides nutritional components, many phytochemical materials in rice have been recognized to involve in biological activities. These bioactive compounds have been associated with several protective effects, such as antioxidant, anticancer, antidiabetic, and anti-inflammation. They have a major effect against chronic diseases and exhibit their potential health benefits in humans.

The performance of nutritional and functional components in rice can be affected by various forms of technology, including breeding, harvesting, processing, cooking, and preservation methods. All the above technologies can be appropriately combined to enhance the different functional properties of rice. Choosing the most suitable technology form for operation is a critical decision, as each technology form has its advantages and disadvantages. Essential factors in determining technology choices are as follows:

  1. Retain or enhance original nutrients;
  2. The developed technology can be industrialized;
  3. The efficiency of production can achieve industrial benefits;
  4. Nutrients or functional components can be effectively ingested by the human body through the employ of different technologies;
  5. Changes in the bio-availability of phytonutrients by different processing techniques;
  6. Food matrix interactions like a binary (starch-lipid, starch-protein, lipid-protein), can influence the nutritional quality, starch retrogradation, gelling, and pasting properties; and
  7. The product's characteristics must be assessed for food safety, ease to use, store and carry.

BREEDING TECHNOLOGY

With smaller genome sizes, rich genetic diversity, and other experimental conveniences, rice is a model crop in plant breeding. Therefore, the genome sequence information has been completed in rice (Sasaki and Burr, 2000), and scientists can use the information to pick specific genes and build planned combinations to accelerate rice breeding performance.

For example, “Golden Rice” was a genetically modified crop developed by the Philippines’ Department of Agriculture Rice Research Institute (DA-PhilRice) in collaboration with the International Rice Research Institute (IRRI). It is considered the most economical way to deal with vitamin A deficiency in developing countries where the primary food is rice. Genetic engineering technology is being employed to obtain extra levels of beta-carotene in rice, which the human body can convert into vitamin A. To engineer the pathway toward the β-carotene formation, four plant enzymes, namely phytoene synthase and phytoene desaturase, ζ-carotene desaturase, and lycopene β-cyclase, have been constructed to yield provitamin A (Tang et al., 2009). The precursor of vitamin A contained in golden rice through enzymatic action in the alimentary canal was converted into substances that the human body can use. Finally, beta-carotene in the Golden Rice was converted into vitamin A, which further improves the body's immune response to diseases.

HARVESTING TECHNOLOGY

Mature rice grains would be subjected to shelling and milling processes to obtain the polished grains that are the softly typical type for the human diet. However, the degree of milling influences the nutrient composition of rice grains since bran which contains more beneficial nutrients than endosperm is mostly excluded during the milling process. Many bioactive compounds do not uniformly exist in a cereal grain but are concentrated in the husk and bran layer. Brown rice grains contain about 5-17% protein (based on a dry base), which would decrease after the strict degree of milling. The contents of dietary fiber and functional matters in brown rice are higher than in white rice because those nutrients mainly exist in hull, bran, and germ. Furthermore, brown rice showed higher contents of minerals, vitamin B complex, and tocochromanols than white rice, resulting in desirable health benefits beyond essential nutrition and reducing the risks of many chronic diseases. Although brown rice contains more beneficial nutrients, it is not popularly associated with acceptable standards to the consumers because of its rough texture.

However, immature rice could be consumed as a whole grain due to its comparatively soft texture and good palatability. Meanwhile, immature rice has different nutritive compositions when compared with mature grains. During grain development, there are apparent changes in phytochemicals, either in their amounts of metabolites. A comparison of the parts of nutrient components depending on their harvest time has been conducted using two Korean rice cultivars (Ji et al., 2013). In this study, the rice grains harvested on the 15th and 25th day after heading (DAH) were considered immature grains, while the one at the 40th DAH was considered mature. The results showed that the contents of Vitamin C and provitamin A were found only in immature rice grains of the two rice cultivars. The immature rice grains contained a higher vitamin B complex level than mature grains. γ-tocochromanols content in immature grains was higher than that in mature grains. Besides, the results also showed that the highest level of reducing sugar was detected in the 15th DAH rice grains, which resulted in those immature whole grains which may have better taste in the aspect of sweetness compared with mature ones. The contents of vitamin C and β-carotene decreased from the 15th to 25th DAH grains, and both components were not detected in the 40th DAH mature grains. This research confirmed that immature whole rice grain might be a good supplement ingredient of provitamin A and vitamin B complex in daily diet. And based on the results, immature rice grains have the potential to be used as the main ingredient of functional food.

Scientists also used two developing rice grains, KFSW (a waxy indica red rice) and TK16 (non-waxy japonica rice), to demonstrate the change of bioactive compounds in immature grains. The study found that the developing rice grains contained more soluble-ester ferulic acids and soluble dietary fiber than the mature ones. Especially the grains on 15th and 18th DAA (days after anthesis) contain high contents of free and soluble-ester ferulic acids, soluble dietary fiber, total tocols, and oryzanols (Lai and Lin, 2010). The research indicated that immature rice grains are a rich source of phytochemicals, which would be attractive in food processing because of the novel features in nutritional properties.

GERMINATION TECHNOLOGY

Germination of grain is a process that modifies starch digestibility and improves bioactive compounds. During the process, the phenolic acids may express important nutritional and technological characteristics of starch-phenolic interactions. This character impacts human physiological performance via the mechanism of delayed digestibility and glycemic control. Studies also have shown the germination treatment of brown rice will increase the content of γ-aminobutyric acid (GABA) in sprouted brown rice. GABA is a non-protein amino acid widely distributed in plants, animals, and microorganisms (Oliveira et al., 2022). It is synthesized as a metabolic product of plants and microorganisms by germination or fermentation. GABA is the major inhibitory neurotransmitter in the mammalian central nervous system that directly affects personality and stress management (Cho et al., 2007; Choi et al., 2006). Some studies have indicated that GABA can lower blood pressure and anxiety, calm the human body and improve insomnia by taking an appropriate dosage in vivo trial. Moreover, GABA offers diuretic and antidiabetic effects (Adeghate et al., 2002). Since GABA has heat-resistant properties that can be used to produce functional food, its physiological activity was conserved even through heat treatment.

PROCESSING TECHNOLOGY

Rice milling

There are many ways to enjoy rice, such as steamed rice, rice balls, fried rice, or porridge. Processing of rice is generally applied in the form of rice grains or rice flour. The rice milling method for rice flour is the most critical step, and the current trend of technology is mainly divided into dry milling, semi-dry milling, and wet milling (Figure 1). Rice flour's physical and chemical properties (such as particle size and damaged starch ratio) are affected by the different methods that further influence the processing conditions, product quality, and functional characteristics. Moreover, the rice flour types are divided into raw and cooked through thermal processing. The main difference between the rice flour in various processing is whether the starch is gelatinized or not (Su, 2014).

Concerning the advancement of processing technology, there are more types of rice products which are showing more and more diversification and increasing demand for processed rice products by consumers, such as noodles, Chinese pasta, biscuits, fried, baked, snack foods, etc. Properly adjusting the material's physicochemical properties, such as suspension, hygroscopicity, swelling, crystallinity, viscosities, and low oil absorption, were the key factors in making rice food products. Novel processed rice products can provide new taste sensations and enhance nutritional value and functional features. The rice flour is highly compatible with the food processing equipment and operating systems, and this character also increases the applications in the food industry.

Extrusion Technology

Convenience foods of the highest quality in terms of natural flavor and health and free of additives and preservatives are what consumers demand for today. The typical case is instant rice with easy portability, quick rehydration, and good nutritional quality. It can be reconstituted into rice grains using rice flour as raw material via the extruder. Another cooking technique for making instant rice is cooking, gelatinization, cooling, and drying using rice grains. If the rice flour is chosen for extrusion processing, the formula can add stabilized rice bran to increase dietary fiber content and trace elements. The rice flour can also be fermented to form the type III resistant starch (RS) first, and then extruded into an instant rice product with low glycemic properties. The same extrusion technology can be operated to make gluten-free whole rice pasta by changing the extrusion die (Figure 2).

Enzymatic and fermented treatment

It is known that gluten-free food like rice and bean tend to fit a natural lifestyle for the consumers. In recent years, researchers have been striving to study grain's effects on the physical properties of grain flour and the manufacturing factors for developing functional grain products. In some researches, the functionality increased rice based product was developed by mixing enzymatic treated rice and protein source with fermented soybean and then further subject to gelatinization, blanching, and forming by extrusion. This novelty process could increase the RS yield of heat resistance by about 26 times and six times of GABA yield in the product and the value of the output. Simultaneously, the standardization process condition has been established, and several product types with health issues, including gluten-free pasta and instant grain meal (Fig. 3). The texture analysis and sensory evaluation show that the experimental group is, on average, equivalent to the control group (Su, 2015).

High pressure processing (HPP) technique

High-pressure processing (HPP) is a relatively new non-thermal food processing method that subjects liquid or solid foods, with or without packaging, to pressures between 50 and 1,000 MPa. HPP could be a helpful tool in increasing the nutritional content of polished rice, especially in increasing the natural thiamine (vitamin B1) content in polished rice (Balakrishna and Farid, 2020). The process of white rice involves the husking of paddy, followed by polishing to remove the bran layer. Rice bran is higher in dietary fiber, vitamins, and minerals, especially the B complex. A recent study reveals that the anti-inflammatory properties of the vitamin B complex may help with hyperphosphorylation and cognitive impairment caused by 1,2 diacetyl benzene (Nguyen et al., 2022). However, brown rice does not have a long-term shelf-life because it is easy for oxidation to happen due to the presence of unsaturated fatty acids in the bran layers. The oxidation of bran layers would possess an off flavor which would decrease the customers' acceptance.

HPP is known to make the rice starch gelatinized, and the bran layers' nutrients get into the endosperm by the HPP. Therefore, scientists deal with paddy rice by utilizing HPP and obtaining rice with higher amounts of natural thiamine. The research results also indicate that the degree of gelatinization and crystallinity, respectively, is subjected to the regulating temperature, pressure and time during HPP. The rice samples were analyzed for thiamine content using the fluorometric method and found that thiamine increased significantly at higher temperature and pressure conditions (Balakrishna and Farid, 2020). HPP treatment showed good potential for enhancing thiamine in white rice with better sensory attributes.

Others

Due to the processing characteristics, rice flour is often compared with wheat flour in terms of price and marketing. To increase the willingness of the key actors in the food industry to use rice raw materials for processing, the research institute in this field must concern itself regarding the industry's and consumers' needs. Refer to the following cases (Su, 2014):

  1. Compared with flour, rice flour has the effect of low oil absorption when used in manufacturing baked or fried products, which can reduce the use of oily materials and human calorie intake;
  2. Rice flour is used to make cold chain food with an anti-freeze and thickening effect, which can replace modified starch and reduce the use of food additives; and
  3. Rice flour can replace flour to make noodle products, which can shorten the cooking time, reduce energy consumption, and offer gluten-free and hypoallergenic properties.

In conclusion, the application of rice has explosive potential in various fields. Scientists are also actively developing technologies in multiple ways.

CONCLUSION

Rice consumption per capita has gradually declined in Asian countries due to changes in dietary habits influenced by western diets, such as increased consumption of high protein and fat meals (meat, egg, and dairy products). However, the COVID-19 pandemic and climate change have significantly impacted the global food industry’s structure. In the future, rice will come back to become an essential part of the Asian diet. The current food crisis has also spurred a revisiting of the self-sufficiency goals of rice. Rice-producing countries must adjust their policies by emphasizing productivity, quality growth, and carbon emission reduction issues to ensure adequate food supplies for the people and sustainability of agricultural surroundings. Food processing technology can enhance many functional properties of rice to form consumption incentives. There is a need to strengthen the applicability of rice through processing and establish a value perception to increase the consumers' willingness to buy rice products in the market. It would be one of the countermeasures to regulate pressure on rice supply and demand.

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