核桃分级破壳取仁及壳仁分离关键技术与装置研究进展

Research progress of key technology and device for size-grading shell-breaking and shell-kernel separation of walnut

中国是世界核桃种植面积和产量第一大国,高营养和经济附加值的核桃精深加工产品需求量日益增加,因而核桃具有广阔的综合开发利用前景。核桃分级、破壳取仁和壳仁分离是初加工流程中最为关键的3个环节,而且是核桃精深加工必备的前道工序。然而传统的手工作业方式及功能简单的核桃初加工装置无法满足食品工业对核桃高品质及批量化要求,严重制约核桃产业的发展。因此,加大核桃初加工关键技术及装置的研发力度势在必行。对于核桃分级,以尺寸特征为基础,锥辊式、栅条式、筛网式、视觉成像式是分级装置的4种原理。基于分级原理,分类总结分级装置现状及其应用特点;不同类型装置的多因素性能试验可得到各自优化参数组合。对于重点环节破壳取仁,核桃相应物理特性是破壳装置设计的重要依据,如球度、壳厚、含水率等直接影响核桃壳、仁的机械性能,分类总结表征不同物理特性的参数值范围。基于物理特性,挤压式、碰撞式、气爆式是核桃破壳的3种主要原理,分类总结核心破壳机构特征及其应用,并重点介绍了3种创新型破壳装置与工作原理。多因素性能试验可优化各类型装置主要影响因素的参数组合。对于壳仁分离,风选式是目前相关装置的主要应用原理,核桃混合壳仁形态特征及物理参数是设置风速和风向的主要依据;在风选式壳仁分离机理的基础上,分类总结多种壳仁分离装置及各自多因素性能试验下的优化参数组合。该研究通过对核桃初加工3个关键环节各自对应的核桃物理特性、工作机理、装置及其性能优化试验进行系统性总结和综述,期望加深对核桃初加工过程的理解,为提升核桃加工水平提供理论依据与技术支持。

Walnut varieties are rich with the wide planting area in China,and the high yield ranked in the world.The walnut kernel is the most important edible part of walnut fruit.The by-products of walnut,such as walnut shell,have also great application potential to serve as cheap raw materials for the extraction of some important medical ingredients and the production of industrial products.However,the by-products are often burned or discarded as wastes in the processing process,leading to environmental pollution.The intensive processing of walnut products is increasing daily demanding with high nutrition and economic added value,indicating the walnut has a broad prospect of comprehensive development and utilization.Walnut size-grading,shell-breaking and kernel-fetching,as well as shell-kernel separating are the most critical the links in the primary processing,which are the prerequisite before the intensive processing of walnut.However,the traditional manual operation mode and the primary processing equipment with simple functions cannot meet the high quality and quantitative requirements of the food industry,which seriously restricts the development of the walnut industry.Therefore,it is imperative to strengthen the research and development of key technologies and devices for walnut primary processing.Based on the size characteristics,four devices were used in walnut size-grading,including the type of taper roller,grid cylinder,sieve,and visual imaging.The status quo and application characteristics of devices were summarized in this review.The combinations of optimized parameters can be obtained from the multi-factor performance tests for different types of devices.The physical characteristics of walnut were important basis for the design of shell-breaking device,such as sphericity,shell thickness,and moisture content,due to they directly determine the mechanical properties of walnut shell and kernel.The specific ranges of parameters were determined to represent different physical characteristics.Three main principles of walnut shell-breaking were then classified,including extrusion,collision,and gas explosion.The characteristics and applications of core shell breaking were reviewed,with emphasis on three innovative shell-breaking devices.The multi-factor performance test can be used to optimize the parameter combination of main influencing factors in each type of device.In shell-kernel separation,the winnowing type was the main application in the relevant devices at present.The morphological characteristics and physical parameters of walnut mixed shell-kernel were the main basis for setting the wind speed and direction.An attempt was made on the separation mechanism of shell-kernel by winnowing type,the optimization parameters of various shell-kernel separation devices and their respective multi-factor performance tests.This review systematically summarized the physical characteristics,working mechanism,device,and performance optimization test,corresponding to the key links of walnut primary processing.The finding can be expected to deepen the understanding of walnut primary processing,and further provide theoretical basis and technical support for improving walnut processing level.