Recent Advances on Application of Radio Frequency Heating in the Research of Post-Harvest Grain Storage and Processing

doi:10.12133/j.smartag.2021.3.4.202106-SA001

Abstract

Abstract:

The storage and processing of grain are the basis for economic and social stability and development. As a new heating treatment technology based on electromagnetic wave, radio frequency technology has the characteristics of large penetration depth, rapid heating, volumetric heating and no chemical residue. It has been widely used in post-harvest research of grain and has potential industrial application prospects in some fields. To expound the research progress of the application of radio frequency heating technology in grain storage and processing, this review briefly described the basic principle and characteristics of radio frequency heating as well as the current commercial radio frequency heating system including free oscillation type and 50 Ω type. The basic research of radio frequency heating in grain storage and processing was summarized from three aspects: Dielectric properties of grain and pests, heat resistance of stored grain pests and heating uniformity of sample. The dielectric properties refer to the interaction between materials and electromagnetic waves in an electromagnetic field and determines the absorption and conversion of electromagnetic energy. It can predict the heating characteristics of grain and provide basic data for computer simulation to optimize process during radio frequency treatment. The heat resistance data of pests are necessary for the establishment and optimization of dis-infestations technology, so the kinetic date of thermal death of common stored grain pests were reported in this review. As a main hinder in the commercial application of radio frequency treatments, the heating uniformity has significant effect on heat treatment quality and results in potential food safety problems. The major factors causing heating non-uniformity are the non-uniformity of electromagnetic field, runaway heating and the sample shape effect. The improvement methods of heating uniformity were summarized from three aspects in this article including changing the electromagnetic field distribution, sample position, and optimizing the radio frequency working parameters. Based on the above basic research of radio frequency technology and combining with the practical problems in grain storage and processing, the applications of radio frequency heating in the fields of dis-infestations, sterilizing, enzyme inactivation and drying were also summarized. Finally, some suggestions on the application of this technology in grain storage and processing and future research directions were proposed. This review may play a certain guiding role for the application of radio frequency technology in grain storage and processing.

Key words: radio frequency heating, post-harvested grain, disinfestation, pasteurization, enzyme inactivation, drying

CLC Number:

TS255.36

LI Hongyue, LI Qingluan, ZHENG Jianjun, LING Bo, WANG Shaojin. Recent Advances on Application of Radio Frequency Heating in the Research of Post-Harvest Grain Storage and Processing[J]. Smart Agriculture, 2021, 3(4): 1-13.

Figures/Tables 8

Fig. 1

Fig. 2

Table1

Fig. 3

Fig. 4

Table 2

Application of radio frequency heating technology in disinfestation of post-harvest grain and their products

粮食种类	主要研究结果
小麦	射频加热至热点达80 °C，冷点处锈赤扁谷盗成虫完全死亡，幼虫在55~60 °C完全死亡。小麦发芽率随水分增加降低，面粉品质无显著变化^［58］；
小麦	射频加热至60 °C，谷蠹、赤拟谷盗、长角扁谷盗、玉米象成虫死亡率达90 %以上，小麦水分、淀粉含量、面筋值等品质指标无显著变化^［59］
稻谷	传送带模式下射频加热至54 °C后保温11 min，谷蠹成虫完全死亡，15 kW系统处理量313.6 kg/h，稻谷除水分降低外，其它物化指标均无显著变化^［60］；
稻谷	传送带模式下射频加热至50 °C后保温6 min，米象成虫完全死亡，6 kW系统处理量224.8 kg/h，稻谷各项物化指标均无显著变化^{［61， 62］}
精米	射频分别加热至45.8、56.9和70 °C，米蛾成虫、幼虫和卵完全死亡，精米主要化学成分、发芽率和感官品质无显著变化^［23］；
精米	射频加热至50 °C后保温5 min，米象幼虫、卵和蛹完全死亡，精米表面无裂纹且感官品质无显著变化，但吸水性和黏度降低^［63］
糙米	传送带模式下射频加热至50 °C后保温6 min，米象成虫完全死亡，6 kW系统处理量247.3 kg/h，糙米各项物化指标均无显著变化^［62］
米粉	射频加热至60 °C以上，米象成虫完全死亡，米粉感官品质无显著变化^［64］
小扁豆	在传送带模式下经射频加热至60 °C后保温10 min，豆象成虫可完全死亡，处理量208 kg/h，水分、色泽、发芽率等品质指标无显著变化^［42］
鹰嘴豆	射频加热至60 °C后保温10 min，豆象成虫完全死亡，鹰嘴豆水分、色泽、发芽率等品质指标无显著变化^［65］
绿豆	射频加热至54 °C后保温 6 min，可完全杀死谷蠹成虫，绿豆主要化学组成、发芽率、色泽等品质指标无显著变化^［57］
玉米	射频加热至60 °C，玉米象卵、幼虫、蛹和成虫完全死亡，玉米主要品质指标及蛋白结构无显著变化，且蛋白功能特性有所提高^［66］

Table 2

Table 3

Application of radio frequency heating technology in pasteurization of post-harvest grain and their products

粮食种类	主要研究结果
玉米	射频加热至65 °C后保温10 min，黄曲霉菌减少3~4 log CFU/g，玉米色泽、发芽率无显著变化，超氧化物歧化酶、过氧化物酶等活性增加^［67］；
玉米	射频加热至70 °C后保温12 min，黄曲霉菌减少6 log CFU/g，玉米水分、蛋白、淀粉等主要化学组成、电导率、发芽率等指标受到显著影响^［68］
玉米粉	射频加热至85 °C后保温10 min，继续置于-20 °C下48 h，肠炎沙门氏菌和粪肠球菌分别减少6.59和4.79 log CFU/g^［69］
小麦	射频加热至65 °C后保温10 min，黄曲霉菌减少2~3 log CFU/g，小麦色泽、发芽率受到显著影响，但超氧化物歧化酶、过氧化物酶等酶活增加^［67］
小麦粉	射频加热至75 °C后自然冷却，水分活度0.25~0.65的面粉中肠炎沙门氏菌分别减少3~7 log CFU/g^［70］；
小麦粉	射频加热至80 °C后自然冷却，粪肠球菌减少1.2~4.6 log CFU/g。Bigelow模型是射频杀菌最优模型，其D值为8.3 min，z值为11.7 °C^［71］
混合谷物粉（Misugaru）	射频加热120 s后，大肠杆菌、鼠伤寒沙门氏菌、蜡样芽孢杆菌的营养细胞分别减少4.68，3.89和4.54 log CFU/g。若采用射频加热120 s并协同1.9 kJ/m²紫外线处理3 min，可使大肠杆菌和鼠伤寒沙门氏菌分别减少5.39和4.76 log CFU/g^［72］
稻谷	射频加热至70 °C后保温3 min，可有效杀灭储粮害虫与霉菌，稻谷淀粉酶活性有不同程度增加，黏度和发芽率无显著变化^［73］
米粉	射频加热至100 °C后保温1 min，菌落总数低于检出限，米粉感官品质无显著变化^［64］
大麦苗粉	射频加热至80 °C后自然冷却，菌落总数减少3.87 log CFU/g，大麦苗粉抗氧化特性、色泽、风味等指标受到显著影响，但优于相同温度下热风处理样品^［74］

Table 3

Table 4

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粮食种类	含水量/（w.b. %）	温度/°C	介电特性数据
粮食种类	含水量/（w.b. %）	温度/°C	介电常数	介电损耗	穿透深度/cm
小麦（锈扁谷盗成虫）^{［20，21］}	15.0（49.0）	15	4.0	0.1（8.0）	——
		45	4.9	0.2	——
		75	6.0	0.6	——
小麦粉（印度谷螟幼虫）^{［18，22］}	12.6（74.0）	25	5.6	0.5（211）	——
		55	6.6	0.6	——
		85	23.5	9.74	——
精米（米象成虫）^{［23，24］}	11.4（47.0）	25	8.8	0.6（48）	1063
玉米粉（杂拟谷盗成虫）^{［25，26］}	10.3（42.0）	20	3.7	0.1（19）	1083
玉米粉（杂拟谷盗成虫）^{［25，26］}	10.3（42.0）	80	8.4	0.7	289
豇豆（四纹豆象成虫）^［27］	12.7（71.0）	20	3.6	0.3 （185）	1008
		40	4.1	0.5	766
		60	5.5	1.0	431
绿豆^［27］	10.2	20	3.2	0.2	1075
		40	3.5	0.3	1063
		60	4.2	0.4	977
麦胚^［28］	11.3	25	3.6	0.4	831
		55	5.8	0.6	623
		85	9.3	0.9	471
米糠^［29］	10.4	25	2.8	0.2	1001
		70	4.9	1.9	213
		100	11.5	12	55

粮食种类	主要研究结果
米糠	射频加热至92 °C后自然冷却，脂肪酶活性降低至18.2 %，米糠蛋白功能特性得以改善^［75］
	射频加热至120 °C后自然冷却，脂肪酶活性降低至1.3 %，但米糠色泽变深，营养物质有所损失^［76］
	射频加热至100 °C后保温15 min，脂肪酶和脂肪氧化酶活性分别降低至19.2和5.5 %，米糠油品质无显著变化但蛋白质二级和三级结构发生改变^{［77， 78］}
麦胚	射频加热至100 °C后保温15 min或110 °C后保温5 min，脂肪酶活性分别降低至18.2 %和22.5 %，麦胚物化特性优于蒸汽处理样品^［79］
大豆	射频加热210 s，脂肪氧化酶活性降低至5.7 %，大豆蛋白的溶解性增加，豆奶风味中己醛与正己醇含量均显著减少^［80］
大豆	射频加热300 s后，脂肪氧化酶、脲酶和胰蛋白酶抑制剂活性分别降低至4.8 %、6.6 %和10.6 %，大豆物化特性得以改善^［81］