Nutritional composition of underutilized bayberry (Myrica rubra Sieb. et Zucc.) kernels

Abstract

The kernels of five bayberry cultivars (Biqi, Zaodamei, Ding-ao, Dongkui and Wandao), grown in Zhejiang Province, China, were analyzed for their proximate composition, protein fractionation, amino acid profile, fatty acid composition and mineral contents. The antinutritive compounds, tannin and cyanide, were also quantified. These bayberry kernels possessed 25.0–27.64% DW protein. A majority of storage protein in bayberry kernels was of the globulin form. The kernel protein was rich in methionine, arginine, aspartic and glutamic acids while limiting amino acid was lysine. The most outstanding feature was the abundant fat content (62.5–68.1% DW) of kernels. Approximately 84.9–90.1% of the fatty acids were unsaturated with oleic acid (43.3–50.7%) and linoleic acid (34.1–46.8%). Bayberry kernels were good sources of magnesium, potassium and calcium. These results may offer a scientific basis for use of the under-exploited bayberry seeds.

Introduction

Bayberry (Myrica rubra Sieb. et Zucc.) is native to eastern Asia, mainly in China, the family of Myricaceae (Chen, Xu, & Zhang, 2004). In China, it is cultivated mainly in south of the Yangtze river, where it is of considerable economic value. The fruit of the Chinese bayberry is red, purple, white, or pink in colour when ripen, depending on the cultivar. It is a small drupe and composed of a fleshy pericarp comprising individual segments and a hard endocarp protecting a single kernel (Miao & Wang, 1987).

Chinese bayberry fruit fleshes contain rich nutritional compositions such as carbohydrate, organic acid, vitamins and so on (Gong et al., 2004, Miao and Wang, 1987, Wang et al., 2001, Xia and Cheng, 2005), and are rich in anthocyanins as well as flavonols and exert strong antioxidant activity (Bao et al., 2005, Ye et al., 1994). Besides being consumed fresh, the bayberry fruit can be made into various products such as juice, wine, jam and canned fruit. In some Chinese bayberry fruit processing industries, bayberry seeds are byproducts and discarded without further utilization.

Bayberry seed is a small stone in which a typical kernel is contained. A few works have been done on bayberry kernels. Zhang, Wang, Zhang, and Xu (1993) found there are some unknown compounds in Chinese bayberry kernels that can inhibit the growth of cancer cells or induce cell death. Zou (1995) isolated and identified bayberry kernels contain quercetin and myricetin. These compounds have antimicrobial and antioxidative activities according to previous studies (Burda and Oleszek, 2001, Cushnie and Lamb, 2005). Base on above reports, bayberry kernel possesses some bioactive substances and is worth to further investigation. Chen, Xu, and Xia (2004) determined the fatty acid composition of bayberry kernel with GC/MS (cultivar Biqi). Results exhibited this kernel could be used as potential oilseed source. However, other nutritional information of bayberry kernel such as protein, amino acid profile, mineral, etc., is still lacking.

Recently, more attention has been focused on the utilization of food processing by-products and wastes, as well as under-utilized agricultural products. Zhejiang is the top area in China producing bayberry fruit, with an annual production over 300,000 tons (data provided by Zhejiang Agricultural Office). The amount of bayberry stones, which comprise 10% or more by the weight of the bayberry fruits remaining after being processed, is quite large. At present there is not a systematic collection and utilization of this material. The bayberry kernel has remained underutilized because of limited information on the detailed chemical composition and nutritional value. The aim of this work was to analyze the nutritional composition of bayberry kernels of five cultivars grown in Zhejiang Province, China, and thereby determine the nutritive value of this byproduct in food or feedstuff.