Rice Bran and Rice Bran Oil

Chemistry, Processing and Utilization

Ling-Zhi Cheong, Xuebing Xu

• Publisher: Academic Press and AOCS Press
• Year: 2019
• ISBN:
  9780128128299
• Topic: Ciencias biológicas
• Subtopic: Ciencias en general

Rice Bran and Rice Bran Oil (RBO) provides much-needed best practices on the science and technology of RBO, including the chemistry, dectection methods, nutrition (including the effect of processing technologies on micronutrients) and applications. RBO contains many nutritional components, including up to 2% oryzanol, tocotrienol, and phytosterols. In addition, the fatty acid composition is well balanced with mainly oleic acid and very little linolenic acid, which allows for versatile uses in frying, cooking, and in formulating oil blends for food uses, especially as a trans-free alternative. Many food industrial sectors are seeking possibilities to use RBO in their products from not only Asia and South America, but also Europe and North America. However, there are many processing, analytical, and nutritional considerations that must be documented in one resource. This volume is perfect for those interested in understanding the many emerging potential uses for this alternative oil.

Written by a team of experts from academia and industry, this book is the first of its kind. In addition, it provides an overview of related rice bran products and their development, including:

• Rice bran protein • Rice dietary fiber • Dietary rice bran/meal • Rice husk/ash applications • Paddy straw applications • Valued added products, including rice bran wax

• Delivers practical application guidance in the selection and storage of raw materials, ensuring processing conditions address stability concerns during production
• Presents simple and reliable detection methods, as well as the international and national rice bran oil standards
• Provides core scientific insights into this trans-free oil option

Chapter 1

Chemistry of Rice Bran Oil

Nurhan Turgut Dunford Oklahoma State University, Department of Biosystems and Agricultural Engineering, Robert M. Kerr Food & Agricultural Products Center, Stillwater, OK, United States

Abstract

Although, it is not widely used as a cooking oil worldwide, demand for rice bran oil (RBO) as a “healthy oil” in specialty applications and functional foods has steadily increased. Chemical composition of bran depends on rice variety, treatment of the grain prior to milling, milling technology used, degree of milling, and the downstream processing of bran, that is, fractionation. Typical oil content in rice bran varies between 10% and 23%.

In general, saturated fatty acid content of RBO is quite high. Palmitic acid is the major saturated fatty acid. Unsaturated fatty acids comprise most of the fatty acids in RBO (55%–87%). Monounsaturated fatty acid, oleic acid, is the most abundant unsaturated fatty acid (38%–48%), followed by polyunsaturated fatty acid linoleic acid (16%–36%). Free fatty acid (FFA) content of RBO varies significantly depending on the quality of bran used for oil extraction. In general, FFA content of RBO is between 2% and 5%. However, extremely high FFA contents ranging from 15% to 40% have also been reported. The biggest challenge for the economic feasibility of RBO is its very high FFA content, which results in extremely high oil losses during refining. Advanced technologies involving supercritical fluid technology and enzymatic reactions have the potential for neutralizing FFA with minimal neutral oil loss.

Due to the limited availability and high nutritional value of RBO, niche markets such as functional foods and nutraceuticals, and high value applications in cosmetics and pharmaceutical appear to be more plausible avenues than renewable fuel applications for expanding RBO markets.

Keywords

Rice bran oil; Fatty acid composition; Oil quality; Free fatty acid content; Oil oxidation; Rice bran oil chemical reactions

1 Introduction

Rice (Oryza sativa L.) is a member of the Poaceae or Graminaceae family native to southeast Asia. It has been cultivated as a food crop for centuries. Rice still is a very important staple food for a large segment of the world's population. It is commonly consumed as milled or white rice, which is produced by removing the hull and bran layers of the rough rice kernel during the dehulling and milling processes, respectively. The bran, which comprises 3%–8% of the kernel and contains pericarp, aleurone, and subaleurone fractions, is a valuable byproduct of rice processing because it contains a high concentration of health beneficial bioactive compounds, including edible lipids.

Although it is not widely used as a cooking oil worldwide, demand for rice bran oil (RBO) as a “healthy oil” in specialty applications and functional food has steadily increased (Ali and Devarajan, 2017).

Processing aspects, nutritional properties, and various applications of RBO are discussed in the other chapters of this book. This chapter specifically focuses on the chemical composition and other properties of RBO.

2 Oil Content of Rice Bran

Chemical composition of bran depends on rice variety, treatment of the grain prior to milling, milling technology used, degree of milling, and the downstream processing of bran, that is, fractionation. Typical oil content in rice bran varies between 10% and 23%. Genotype significantly affects the oil content in bran (Goffman et al., 2003). Oil contents of a collection of 204 rice accessions grown in Beaumont, Texas, USA were examined. A genetically diverse germplasm collection including historical and present-day U.S. cultivars, as well as Asian, European, South American, and African rice cultivars, were included in the investigation (Goffman et al., 2003). Oil contents of the genotypes examined varied from 17% to 27%. Over 75% of the lines had oil contents higher than 22% (weight/weight [w/w]). Another study examining 15 rice varieties grown in Ghana (Amissah et al., 2003) revealed that oil content in the samples (13%–20%) was similar to the oil content reported in other varieties (Goffman et al., 2003). Glutinous rice is shown to contain more oil than nonglutinous brown rice (Taira, 1984).

The degree of milling has a significant effect on the oil content of bran (Saunders, 1985). For example, 0%–8% milling produced bran with about 17%–18% oil content, whereas increased milling from 6%–9% to 9%–10% decreased the oil content from 16.5% to 14.2%, respectively. Increased milling contaminates bran with endosperm, which is low in oil content. In general, bran from parboiled rice contains a considerably higher amount of oil than bran from raw rice (Islam et al., 2002; Rao et al., 1965). According to Rao et al. (1965), oil content of parboiled rice bran was higher (28%–34%) than that in raw bran at 5% degree of milling (24%–26%). The researchers speculated that oil in the aleurone layer migrated to the bran during parboiling and increased the oil content in the bran. Also, bran from parboiled rice contains less starch, increasing the oil fraction in the bran.

3 Fatty Acid Composition of Rice Bran Oil

Similar to the other grains and oilseeds, chemical and fatty acid compositions of rice vary substantially with variety, agronomic practices, and environmental conditions. The studies on 24 lowland nonglutinous rice varieties grown on the Hiroshima Agricultural Experiment Station, Japan, in 1976 and 1977 found that variety had a significant effect on stearic, oleic, and linoleic acid contents in bran (Taira et al., 1979). Crop year had the most significant effect on palmitoleic and linolenic acid contents. A significant positive correlation between the daily mean temperature during ripening and palmitoleic, stearic, oleic, and arachidic acid contents was observed. The correlations between myristic, palmitic, linoleic, and linolenic acid contents and daily mean temperatures were negative and significant in year 1976 but not in 1977. The latter results were explained by the lack of significant temperature variation during the 1977 crop year. A significant negative correlation between oleic and linoleic and linolenic acid contents and a positive correlation between linoleic and linolenic acid contents were observed in both years. Although these results indicate the effect of environmental conditions and variety on fatty acid composition, it is important to note that a 2-year study at one location might not be enough to establish reliable correlations.

A study carried out on 204 rice genotypes identified two groups: one with low palmitic acid (< 17.5% with a mean of 16%) and one with palmitic acid in the range of 17.5% and 22% (Lugay and Juliano, 1964). The cultivar Indica had a higher saturated/unsaturated fatty acid ratio (S/U) than Japonica. Another study confirmed the latter findings demonstrating that Indica cultivars, Peta and Malagkit Sungsong Puti, had lower iodin...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• Chapter 1: Chemistry of Rice Bran Oil
• Chapter 2: Nutritional Studies of Rice Bran Oil
• Chapter 3: Processing Technology of Rice Bran Oil
• Chapter 4: Bioprocessing Technology of Rice Bran Oil
• Chapter 5: Micronutrients in Rice Bran Oil
• Chapter 6: Applications of Rice Bran Oil
• Chapter 7: Analytical Aspects of Rice Bran Oil
• Chapter 8: Development of Rice Bran Functional Food and Evaluation of Its Healthful Properties
• Chapter 9: Rice Husk, Rice Husk Ash and Their Applications
• Chapter 10: Nutritional Ingredients and Active Compositions of Defatted Rice Bran
• Chapter 11: Rice Bran Protein: Extraction, Nutraceutical Properties, and Potential Applications
• Index