Morphological and physicochemical characterization of starches isolated from chestnuts cultivated in different regions of China

Highlights

• Physiochemical properties of 21 chestnuts starches were examined.

• Starches presented significant differences in morphology, pasting, and thermal properties.

• Starches from Maoli had generally smaller granule sizes.

• Starches from Youli presented higher resistance to shear and thermal swelling.

• All chestnuts had C-type starch, among which most starches were in C_b-type.

Abstract

This study was to compare the characteristics of 21 starches isolated from chestnuts produced in different regions in China, also to investigate their potential food applications. Starches were isolated from chestnuts under the Castanea mollisima Blume variety with sub-varieties of Banli, Youli, and Maoli. Several properties of the starch samples were examined, including the moisture content, amylose content, morphological characteristics, color values, light transmittance, syneresis, swelling power, water solubility index, pasting properties, FTIR characteristics, X-ray diffraction (XRD) patterns, and thermal properties. The results showed that starches isolated from Youli presented higher resistance to shear and swelling during heating, indicating more suitability for high-heat cooking. The FTIR spectra confirmed the polysaccharide nature of all the chestnut starches. The XRD patterns showed most chestnut starches were in C_b-type, while only five were in C_a-type. Overall, this comparative study would be relevant for the further exploration of the potential utilization of chestnut starch in both food and non-food industries.

Introduction

As the most common carbohydrate in human diets, starch serves as a major energy source and can be found in large amounts in staple foods such as potato, corn, rice, and wheat. Most commercial starches are isolated from these crops through wet milling process. The isolated starches have much utilization as both nutritional food ingredients and functional additives in foods. For instance, based on their characteristics, starch can be used as stabilizers, gel formers, emulsifiers, and thickening agents. In addition, starches can be used to produce sweeteners (e.g., sugars, syrups, and sugar alcohols) and ethanol. Moreover, starch is widely used in non-food applications, e.g., in papermaking, pharmaceuticals, and even mining industries. Therefore, native starch is in high demand for meeting the global needs for the production of various goods, which raises the significance of exploring more botanical sources for starch.

While properties of mainstream starches (e.g., potato and corn starches) have been extensively studied, few have been focusing on chestnut starch, especially a comparative study of that from different regions. The present study was to examine the physico-chemical properties of starches isolated from chestnuts that were harvested in different regions in China. As an important food crop cultivated in many parts of the world, chestnut is a group of fruits belongs to the genus Castanea spp. in the family of Fagaceae, with major sub-species include Castanea mollissima in China, C. crenata in Japan, C. dentata in North America, and C. sativa in Europe [[1], [2], [3], [4]]. It is widely distributed and consumed in Asia, America, and Europe, with an increasing world production during the last few decades. China serves as one of the top producers of chestnuts according to the Food and Agriculture Organization of the United Nations [4]. Under the variety of Chinese C. mollissima, chestnuts are commonly classified into three sub-groups based on their morphological characteristics, which are Banli, Youli, and Maoli in their common names. Banli has an overall large size and flat shape, with a darker mat and unpolished skin, and is the most common chestnut variety in China. Youli, on the other side, presents a relatively smaller size and round shape, and its skin appears deep brown with shiny and glossy surface. Maoli has the smallest size with a hemispherical shape, and its fruit is less plump compared to Banli [5]. Unlike other culinary nuts, chestnuts have very low fat and protein content. Their calories come chiefly from carbohydrates, with almost twice as much starch as in potato on a dry basis [6]. According to studies conducted by Liu et al. [7] and Moreira et al. [8], the total starch content of chestnut fruits (varieties of C. mollissimia) range from 42.4% to 53.8%. Due to its relatively high starch content, it is expected that chestnut quality is highly associated with its starch properties. Further, the chestnut starch may serve as a novel starch source with great potential applications both food and non-food industries [9]. Therefore, the in-depth study of the properties of chestnut starch is of great significance.

The chestnut cultivars in China are mainly grown in the middle regions, north-eastern, eastern, and south-eastern areas of the country, distributed in five basic temperature zones based on their climate characteristics, which are warm-temperature zone, north subtropical zone, mid subtropical zone, south subtropical zone, and tropic zone. Chestnuts are widely cultivated except for a few areas like Qinghai, Ningxia, Xizang, and Xinjiang, while provinces of Hebei, Henan, Liaoning, Shandong, Shaanxi, and Hubei are some famous origin places of chestnuts. Favoring low hills, gentle slopes and river banks, chestnuts grow largely depend on the environmental factors such as temperature, water, soil, and sunlight. In addition, the properties of starches isolated from these chestnuts can also be affected by various environmental factors around where they are grown.

Although there are previous studies on the structural and functional properties of chestnut starches [7,[9], [10], [11], [12]], there have been few comparative studies on the properties of starches isolated from Chinese chestnut varieties in different regions. Therefore, to meet high demand of new-source starches and extend the utilization of chestnut, this study aimed to examine the physical and chemical properties of starches isolated from chestnuts produced in 21 cultivation regions in China and to make comparisons among them, including the moisture contents, morphological characteristics, color values, physio-chemical properties, pasting properties, FTIR spectra, X-ray diffraction patterns, and thermal properties. Information generated from this study will be useful for guiding their potential applications and possible contributions to both food and non-food industry.