Effects of Endogenous Non-Starch Nutrients in Acorn (Quercus wutaishanica Blume) Kernels on the Physicochemical Properties and In Vitro Digestibility of Starch.

Yanwen Wu,Jie Ouyang,Tianyi Ding,Mohe He

doi:10.3390/foods11060825

Abstract

The present study investigated the multi-scale structure of starch derived from acorn kernels and the effects of the non-starch nutrients on the physicochemical properties and in vitro digestibility of starch. The average polymerization degree of acorn starch was 27.3, and the apparent amylose content was 31.4%. The crystal structure remained as C-type but the relative crystallinity of acorn flour decreased from 26.55% to 25.13%, 25.86% and 26.29% after the treatments of degreasing, deproteinization, and the removal of β-glucan, respectively. After the above treatments, the conclusion temperature of acorn flour decreased and had a significant positive correlation with the decrease in the crystallinity. The aggregation between starch granules, and the interactions between starch granules and both proteins and lipids, reduced significantly after degreasing and deproteinization treatments. The endogenous protein, fat, and β-glucan played key roles in reducing the digestibility of acorn starch relative to other compounds, which was dictated by the ability for these compounds to form complexes with starch and inhibit hydrolysis.

Highlights

Acorn is a general name for the fruit of the Fagaceae family of oak trees and their close relatives, which are widely distributed throughout the northern hemisphere
The amylose content in Q. wutaishanica measured in the present study was 33.1% of starch, which was similar to one previous report [1] and lower than the amylose content in peas (41.1%), lentils (38.0%), and broad beans (39.9%) [31]
From the Scanning Electron Microscopy (SEM) images, the particles attached to the surface of the starch granules were most likely protein molecules because the degreased acorn flour (DGAF) and de-β-glucan acorn flour (DβAF) starch samples had rough surfaces, while the surfaces of the acorn starch (AS) and deproteinized acorn flour (DPAF) starch samples were smooth

Summary

Introduction

Acorn is a general name for the fruit of the Fagaceae family of oak trees and their close relatives, which are widely distributed throughout the northern hemisphere. There are seven genera and 900 species within the Fagaceae throughout the world, including Fagus, Castanea, Castanopsis, Lithocarpus, Trigonobalanus, Quercus, and Cyclobalanopsis. Acorns have a long history of being used as a raw material in staple foods in Northern China, with an annual harvest in China of 6–7 million tons [1]. Fresh acorn contains about 42% moisture, 49% starch, 4.2% protein, 5.2% fat, 1.7% ash and 2.7% fibre in several Quercus species [2]. A total of 12 fatty acids have been detected in acorns, among which linolenic acid, linoleic acid, and palmitic acid were the most abundant. 17 amino acids, including five essential amino acids, have been detected in acorns [3,4]. Acorns have good potential as an alternative functional food and their by-products are valuable [5]

Methods

Results

Conclusion