Radiation preservation of foods of plant origin. Part 2. Onions and other bulb crops

The various factors contributing to post harvest losses in onions and other bulb crops are briefly outlined in terms of the current storage methods. The present status of research on sprout inhibition by irradiation is reviewed in detail with respect to dose requirements, effect of time interval between harvest and irradiation, and the influence of environment on sprouting during storage. Biochemical mechanisms of sprout inhibition, metabolic and compositional changes (particularly sugars, anthocyanins, flavor and lachrymatory principles), and the culinary and processing qualities of irradiated onions are discussed. The future prospects for the commercial irradiation for sprout inhibition of bulb crops are considered.     

The effect of gamma irradiation on glycoalkaloid and chlorophyll synthesis in seven potato cultivars

The use of gamma irradiation to control sprouting and increase the length of storage time of potatoes has been proposed as an alternative to cold storage or the use of chemical sprout suppressants. Indeed, it is applied on a commercial-scale to potatoes in Japan. This research reports on the effects of different levels of gamma irradiation on seven potato cultivars in relation to chlorophyll and glycoalkaloid synthesis on subsequent exposure to light after a period of storage. There were significant genotype differences between cultivars in their response to gamma irradiation, with some cultivars exhibiting dramatically reduced levels of glycoalkaloid synthesis compared with others. Also, cultivars responded differently to variable irradiation levels. The implications of the results are discussed in relation to public health concerns and selection within potato breeding programmes. © 1997 SCI.     

Experiences of food irradiation in Japan

Abstract

In this paper, we shall attempt to present the history and current status of food irradiation research and commercialization in Japan. In 1967 the Japan Atomic Energy Commission decided to promote the research and development of food irradiation, based on research activities since 1954. The national project on food irradiation investigated the following: 1) the inhibition of sprout growth of potatoes and onions, 2) the prevention of infestation of rice and wheat, 3) the extension of shelf life of sausage and fish‐paste products, and 4) the growth inhibition of molds on the surfaces of oranges by using electron beams. As a result of this national project, a commercial potato irradiation plant was constructed and has been operating for 12 years. Market price fluctuations during the off‐season were also successfully reduced. However, a boycott movement by some consumer unions against irradiated potatoes has seriously affected food processors. The technical problems of irradiated potatoes, such as rotting and accumulation of sugar during storage, were solved by conditioning before and after irradiation. After the termination of the national project, studies were carried out on farm animal feeds for the purpose of eliminating pathogens such as salmonellae and extending shelf life by delaying mold growth. The accumulation of sugar in irradiated sweet potatoes, identification methodology of irradiated foods, and radiation‐decontamination of microorganisms in spices have also been studied. The greatest problem now is to overcome the public's resistance to irradiated food.     

Effect of irradiation on vitamin C content of strawberries and potatoes in combination with storage and with further cooking in potatoes

The vitamin C content of four varieties of strawberry was determined before and after treatment with ionising radiation at doses of 1, 2 or 3 kGy and after storage for 5 and 10 days at 6°C, and also in potatoes which, having been allowed a period of one month to recover from the effects of post-harvest stress, were irradiated at a sprout inhibition dose of 0·15 kGy, followed by storage and cooking. Total ascorbic acid (TAA), ascorbic acid (AA) and dehydroascorbic acid (DHAA) concentrations were measured using the technique of ion-exclusion high-performance liquid chromatography. Results from analysis of the strawberry samples showed the DHAA content increased immediately following irradiation and must, therefore, be taken into account when reporting vitamin C levels in irradiated produce. In addition it was observed that whilst irradiation did affect the vitamin C concentration in all varieties of strawberry, the change was small in comparison with the large variations observed between varieties. With regard to potatoes results showed that, whilst irradiation, storage and cooking all had the effect of reducing vitamin C concentration, irradiated samples stored for 5 months had similar or marginally higher levels than their non-irradiated counterparts. Cooking did not markedly reduce TAA content of irradiated potatoes compared to non-irradiated potatoes and it was also noted that microwave cooking was more destructive than boiling in lightly salted water. ©1997 SCI     

Gamma Irradiation and Enriched CO2 Atmosphere Storage Effects on the Light-induced Greening of Potatoes

SUMMARY – Michigan-grown Kennebec and Sebago potato tubers were exposed to gamma irradiation in the dose range of 0 to 400 Krad and subsequently stored in atmospheres containing 0.03% to 15% CO₂. Upon illumination with 3,000 lux for periods up to 20 days while maintaining the atmosphere, all tubers developed some greening. The tubers exposed to 200 and 400 Krad were inhibited from greening to the highest degree but suffered general quality loss. The levels of 10 to 20 Krad, which are suitable for the sprout inhibition of potatoes, did not cause significant inhibition of greening under any of the conditions of this experiment. Storage in enriched CO₂ atmospheres inhibited the greening to the extent of 50% at 15% CO₂, only upon prolonged illumination (12 days), while irradiation (40 Krad) was only effective after a short period (4 days) of illumination. Irradiation in the O–40 Krad range did not increase the inhibition caused by CO₂. The inhibition of potato greening by irradiation was effective through a period of 5 weeks storage in the dark prior to illumination.     

高能电子束与60Coγ射线对大蒜辐照保鲜效果的比较研究

我国大蒜辐照抑芽工艺规范没有对60Coγ射线和电子束应用的工艺参数做出区分,为明确两者对大蒜抑芽保鲜效果的差异,以60Co 产生的γ射线和电子加速器产生的高能电子束,分别对大蒜进行辐照处理,辐照剂量为200、500、800Gy,辐照后置于室温(5～25℃,RH 70%～85%)贮藏,并对贮藏期间大蒜内芽生长情况及各生理指标进行测定。结果表明：两种辐照源均能有效抑芽,且相同辐照剂量下,电子束辐照抑芽效果强于60Coγ射线;200Gy 和500Gy 的两种辐照均能抑制大蒜呼吸作用,延缓质量损失,且对大蒜鳞茎外皮颜色和大蒜风味品质影响不大;而高剂量800Gy 的两种辐照则刺激大蒜呼吸增强,失重率升高,大蒜干缩严重。从大蒜营养品质和商业品质的角度综合分析,电子束采用200Gy、60Coγ射线采用500Gy 对大蒜的抑芽保鲜效果较好。     

Histologischer Nachweis einer erfolgten Bestrahlung von Kartoffeln

Zusammenfassung Im Hinblick auf die Möglichkeit einer kommerziell durchgeführten Bestrahlung von Kartoffeln zum Zwecke der Keimhemmung benötigen die mit der Lebensmittelüberwachung beauftragten Behörden eine Methode zur Identifizierung bestrahlter Kartoffeln. Es ist möglich, die bekannte Hemmung der Wundperidermbildung durch Bestrahlung als Nachweis zu verwenden.

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Histological identification of irradiated potatoes

Summary The prospect of commercial irradiation of potatoes makes it necessary to develop methods which enable the responsible government agencies to identify irradiated potatoes. It is possible to use the well known inhibition of wound periderm formation by irradiation for such an identification.

     

静电场结合自发气调包装对马铃薯贮藏期间的保鲜效果

以延长马铃薯的货架期并保持其品质为目的,选用阻隔性材料聚乳酸（polylactic acid,PLLA）薄膜对采后新鲜马铃薯进行自发气调包装,设置无包装的空白组为对照,以低温冷藏为前提（均设置4 ℃、85%相对湿度）,分别置于电场和无电场两组环境贮藏,测定贮藏过程中气体组分、感官评分、质量损失率、a*值、干物质质量分数、可溶性固形物质量分数、淀粉质量分数及VC含量。结果表明：静电场可以显著抑制马铃薯表皮变绿及发芽;PLLA自发气调包装可形成一个相对高CO2体积分数（4.2%～8.0%）和低O2体积分数（7.7%～12.3%）的气体组分;综合了静电场保鲜与自发气调包装的静电场-气调组保鲜效果最佳,该组水分、感官品质保持最好,各项营养成分损失较慢,贮藏150 d仍具有食用价值。因此,静电场和自发气调包装联合处理有利于马铃薯的保鲜贮藏。     

Effect of Sprout Inhibitor Isopropyl-N(3=Chlorophenyl)-Carbamate on Total Glycoalkaloid Content of Potatoes

The effect of the sprout inhibitor, isopropyl-N-(3-chlorophenyl)-carbamate (CIPC) on total glycoalkaloid (TGA) content of potatoes was investigated. Katahdin and Chipbelle potatoes grown at Cornell Research Farms, Freeville, NY and Riverhead, NY, were used. Potatoes treated with CIPC were significantly (p < 0.05) lower in TGA content than the controls. Potatoes stored at 25°C were significantly (p < 0.05) higher in TGA content than those stored at 5°C and TGA content increased significantly (p < 0.05) with increasing storage time.     

Effects of Gamma Irradiation Dose and Timing of Treatment after Harvest on the Storeability of Garlic Bulbs

The effect of gamma irradiation dose and time of treatment after harvest on the storage of garlic bulbs was investigated. The effectiveness of irradiation for external sprout inhibition was not affected by the treatment time within 45 days after harvest. At 285 days after harvest, irradiation of 50 - 150 Gy caused about 6% less decrease in weight loss compared with the unirradiated group, and spoilage rates of the unirradiated and irradiated cloves were 100% and 17 - 20%, respectively. For the overall storageability of garlic bulbs, 75 Gy was shown to be the minimal optimum dose, and there was no apparent effect depending upon the time of irradiation treatment after harvest.     

Identification of irradiated foods by the thermoluminescence of mineral contamination

This investigation assessed the radiation-induced thermoluminescence (TL) of food minerals for identifying irradiated foods. Mineral contamination, rather than the inherent mineral content, of foods was studied. Positive identification of foods given 1-10-kGy doses depends on the contents and composition of the mineral contamination and the time span between irradiation and TL analysis. All 20 irradiated spice and herb samples could be identified without comparing them with unirradiated material. Three out of 60 lots of spices and herbs examined so far were so pure that the mineral contents were too low to allow TL analysis. If the soil where potatoes are grown contains feldspars, sprout inhibition treatment with 100-200-Gy doses can also be detected for up to one year, using the 90-250 degrees C low-temperature part of the TL spectrum for evaluation.     

Evaluation of ethereal extracts of irradiated garlic

The present work describes the results of a comparative study on ethereal extracts of ‘red’ garlic bulbs, both in control samples and samples irradiated with 50 Gy of ⁶⁰Co gamma rays for sprout inhibition. The evaluations were carried out by both gas-liquid chromatography and visible and infra-red spectroscopy.During 180 days' storage post-treatment in a commercial warehouse (Temperature: 6–32°C, RH: 58–86%) no appreciable changes were detected in gas-liquid chromatograms between control and irradiated samples. Neither were any differences in spectral character in the visible and infra-red ranges observed between the two types of samples maintained under similar storage conditions for 90 days after irradiation.     

Sugars and Free Amino Acids in Stored Russet Burbank Potatoes Treated with CIPC and Alternative Sprout Inhibitors

Glucose, fructose, sucrose and free amino acids were measured in stored Russet Burbank potatoes treated with sprout inhibitors isopropyl-N-(3-chlorophenyl) carbamate (CIPC), 1,4-dimethylnaphthalene (DMN), cineole and salicylaldehyde. Storage effects on sugar and amino acid contents were dependent on the specific sprout inhibitor. Salicylaldehyde treatment (200 ppm) produced a rapid increase of reducing sugar content and a greater amount of free amino acids than other treatments. A smaller amount of tyrosine was found in DMN (40 ppm) treated tubers compared to all other treatments. After 16 wk at 7°C, all potatoes treated with inhibitors had 10.5–11.8 mg/g dry weight reducing sugar content which would be considered acceptable for French fry processing.     

Effect of cultivars, wound healing and storage on sensory quality and chemical components in pre-peeled potatoes

This study deals with eating quality of pre-peeled potatoes. The effect of raw material quality (cultivar, duration of wound healing and storage) on chemical composition of raw potatoes, and sensory quality and aroma composition of cooked pre-peeled potatoes were determined. Potatoes were knife peeled, vacuum-packed, stored at 4 °C, and evaluated after 6 days of shelf-life. Significant differences in chemical composition, sensory quality and aroma composition were found among the 6 cultivars. Storage (0, and 6 months) also affected the sensory quality and the aroma composition. For surface hardening an effect of wound healing time (2 or 4 weeks at 14 °C) was observed, since 4 weeks resulted in lower intensity in surface hardening. During long-term storage the intensity in surface hardening decreased. The aroma compounds linalool, methional, nonanal and decanal were correlated to potato flavour and rancidness, whereas off-flavour/off-taste seemed to be correlated to nonvolatile components. Enzymatic browning of potatoes was positively correlated with PPO activity, tyrosin and chlorogenic acid a well as aspartic and glutamic acid, but negatively correlated to caffeic acid. The study showed that the quality of pre-peeled potatoes is very sensitive to raw material quality, and the time of year being processed.     

Combined effect of electron-beam (beta) irradiation and organic acids on shelf life of pork loins during cold storage

The combined effects of organic acids and irradiation on shelf life of pork loins were examined. Fresh pork loins were sprayed with organic acids (lactic, citric, and acetic) at 2%, packaged aerobically, and irradiated with an electron beam at 1, 2, and 3 kGy. During 14 days of storage, total plate count, coliform number, pH, and thiobarbituric acid-reactive substances were measured. Combinations of organic acid and irradiation were more effective in reducing and maintaining low total plate counts and coliform levels during storage than either treatment alone. Higher lipid oxidations were observed in all combination treatments at 1 day of storage than in the irradiation-only group. However, lower lipid oxidations were the result after 14 days of storage when combination treatments were used with irradiations of 2 and 3 kGy. Combined treatments involving lower irradiation doses than those required for irradiation alone could be used to extend the shelf life of pork loins during postirradiation storage without increasing lipid oxidation.     

SPROUT INHIBITION BY GAMMA IRRADIATION IN FRESH GINGER (ZINGIBER OFFICINALE ROSCOE)

ABSTRACT. A study on sprout inhibition by gamma irradiation in fresh ginger of a local variety was carried out. Fresh ginger was irradiated at the doses of 0, 25, 50 and 80 Grays (Gy) and stored at temperature 25-28°C and relative humidity ranging from 76-96% for 4 months. the parameters observed were physiological weight loss, sprouting, external appearance, fungal infection, moisture content, water activity, crude fiber content and total sugar. the results show that irradiation at the doses studied effectively inhibited sprouting in ginger when compared to the nonirradiated samples. However, radiation was unable to extend the shelf-life as all samples started to deteriorate after 2 months storage.     

Effect of Irradiation on Total Glycoalkaloids in Kennebec and Russet Burbank Potatoes

Effect of irradiation and storage conditions following irradiation on total glycoalkaloids (TGA) of Russet Burbank and Kennebec potatoes stored 4 and 12 wk was investigated. TGA increased significantly (p < 0.005) immediately following irradiation in both cultivars, but decreased upon storage. TGA was higher in Kennebec than Russet Burbank often exceeding levels considered safe for human consumption. At 5°C TGA was higher in tubers stored in paper as compared to polyethylene, while at 20°C this was reversed.     

Acrylamide content in fried chips prepared from irradiated and non-irradiated stored potatoes

The content of reducing sugars and asparagine, responsible for the formation of acrylamide, was determined in eight Indian potato varieties. Among these, Kufri chipsona-2 and Kufri lavkar showed the lowest level of reducing sugar (680.68 ± 56.50 mg/kg) and asparagine (2074.36 ± 122.27 mg/kg), respectively. The acrylamide content in potato chips prepared from Kufri chipsona-2, the variety that is used commercially in India for making potato chips was also the lowest. Irradiation of this variety of potatoes at the sprout inhibition dose of 60 Gy and subsequent storage for six months showed a 10.7% lower content of reducing sugars at both 14 and 4 °C. The acrylamide content was 8.41% and 6.95% lower in chips from irradiated potatoes stored at 14 and 4 °C than the corresponding non-irradiated controls. The colour of the chips was also better in irradiated potatoes as judged from the L∗ and a∗ values.     

Food irradiation: is it an alternative to chemical preservatives?

Generalizations about effects of irradiation may be misleading if the dose and commodities are not specified. Irradiation could be used for inhibition of sprouting, disinfestation, destruction of parasites in meat, to delay maturation of fruit and for pasteurization and sterilization. In some applications it could replace chemical sprout inhibitors, fumigants and chemical preservatives; in other cases it may have unique advantages e.g. in eradication of non-spore-forming pathogens in dry or frozen foods. Toxicological and nutritional evaluation has repeatedly confirmed the safety of irradiated foods. Effects on nutritional quality are frequently comparable with heat treatment and sometimes more conservative, particularly if oxygen is excluded. While food irradiation could be an alternative to chemical preservatives, misinformation has led to uncertainties as to its future.     

TEXTURAL GAIN AND SUBSEQUENT LOSS IN IRRADIATED APPLES, CARROTS AND POTATOES WITH INCREASE IN DOSE FROM 0.03 TO 1.0 kGy

Cored samples (16mm × 15mm diameter) of apples, carrots and potatoes were irradiated in an Isomedix Gammacell 1000 irradiator at a dose rate of approximately 9Gy/min. Texture was measured using unrestrained uniaxial compression to microrupture on the JJ Universal Testing Machine. The loading rate was 6mm/min. Texture or firmness was assessed as the force to microrupture; the force required for various microrupture sample deformations (25%, 50% and 75%); the apparent Young's Modulus (ratio of the average stress to the average strain to microrupture); and the microrupture energy (area under the force-deformation curve). As the dose increased from 0.03 up to about 0.1 kGy, a gain in texture generally occurred in all products ranging from 3% to 16%. A transition area from gain to loss occurred within the 0.1 to 0.3 kGy range. Loss of texture occurred in all products as the dose increased from 0.3 to 1.0kGy, the loss ranging from 4% to 30%. The greatest loss of texture occurred in apples and the least loss in carrots. There textural trends may have commercial significance in low dose irradiation processes such as sprout inhibition, senescence delay and disinfestation.