A SCIENTIFIC BASIS FOR BEER FOAM FORMATION AND CLING

The most complex types of nitrogen compound in beer (here termed “proteoses”) are, when not combined with polyphenols, highly surface active and hence concentrate in the foam. With unhopped beer, the foam is of the “liquid-viscous” type, which eventually drains and collapses leaving no residual solids. The iso-α-acids in hopped beers are also surface-active, so they too are concentrated in the foam. At the corresponding concentration in bulk solution the solubility limits of some isohumulates* are exceeded. Thus we believe that solids are similarly formed in the bubble films, so that these are reinforced and stiffened to give “cling”. One consequence of the increased concentration of iso-α-acids in the foam is that there can be precipitation of iron, nickel, cobalt and zinc isohumulates. This results in concentration of these metals in foam. The most significant finding is that the concentration of both proteoses and iso-α-acids in the foam exceeds the bulk solubility limits and results in the formation of proteose-isohumulate salts which make the main contribution to the solid reinforcement of bubble films. These findings make it possible to explain satisfactorily “lacing” or “cling” and also isohumulone losses (a) during boiling and trub separation, (b) during post-fermentation bittering, and (c) during any subsequent foam formation. An explanation is also provided why losses of bitterness and of head retention are linked. Consequently, linked recovery of both bitterness and head retention can occur, as has been found is some recent fermentation improvements, such as continuous fermentation.     

MATURITY STANDARDS FOR PROCESSING CLINGSTONE PEACHES

The flesh color of 5 clingstone peach cultivars was measured (in CIELAB coordinates) by tristimulus colorimeter before and after canning. Before canning, fruit were separated into 3 color classes (1A: green-yellow, 4A: yellow-green, 7A: orange) by visual comparison with a trial maturity chart. After canning, flesh color was measured and visually graded. All samples in color class 1A were rated USDA grade C, while classes 4A and 7A were rated grade A. Flesh color was also measured as a function of time before and after harvest. Fresh flesh L* values were approximately constant, a* values increased steadily, and b* values increased then slightly decreased. Final specifications for a new maturity chart were 7 colors of constant luminance (L*= 76.5) and linearly increasing a* and b* values (?5.0 to 13.0 and 70.1 to 76.4, respectively), corresponding to a time step of 3.5 days between colors.     

PACKING TECHNOLOGY FOR FRESH AND MINIMALLY PROCESSED FRUITS AND VEGETABLES

Flexible plastic packaging in the fresh produce industry has functioned in the past to facilitate product handling and provide brand identification. Greater emphasis on freshness and product quality has resulted in a re-evaluation of plastic for fresh and minimally processed products. Polyvinylchloride, used primarily for overwrapping, and polyethylene, used for bags, have been the most popular films, but co-extrusion technology has provided a means of controlling gas transmission rates. Individual film wrapping represents a rediscovery of an old technique that has applications in prevention of shrinkage and altering of ripening patterns. Modified atmosphere packaging and value added products represent other new technologies that use packaging to extend shelf-life.     

AN EXPERIMENTAL STUDY IN CONSUMERS' WILLINGNESS-TO-PAY FOR AN IRRADIATED MEAT PRODUCT

In a nonhypothetical laboratory experiment, participants were willing to pay an average of $0.71 for the right to exchange a typical meat sandwich for a sandwich irradiated to eliminate the potential risk of foodborne bacteria. Forty-one of sixty participants (68.3%) were willing to pay some positive amount. Tobit analysis was used in order to allow for the fact that Willingness To Pay (WTP) was censored at zero. WTP was interpreted as the demand for irradiation to control foodborne disease. A positive WTP was interpreted as acceptance of irradiation. The aggregated WTP greatly exceeds the estimated direct costs of foodborne disease, and the estimated costs of irradiation for many food products. There was a positive relationship between WTP and the perceived risk of foodborne disease, and a negative relationship between WTP and years of education.     

MONILINIA AND RHIZOPUS DECAY CONTROL DURING CONTROLLED RIPENING OF FREESTONE PEACHES FOR CANNING

ABSTRACT— Decay was controlled when freestone peach fruit, harvested at various stages of maturity ranging from green to straw-color, were dipped in 50% 2,6-dichloro-4-nitroaniline (DCNA) at 1–1/2 and 4 lb/100 gal water and ripened for 5–17 days at 20°C and 90% R.H. Treated fruit had less than 10% decay while untreated fruit developed as much as 61% decay during this period. Regardless of treatment, straw-blush and full-blush fruit held for only 3 days did not develop decay. The most commonly occurring fungus pathogens, Monilinia fructicola and Rhizopus stolonifer, were controlled with these treatments. Postharvest DCNA plus captan dip treatments gave more effective decay control than from preharvest field sprays. Concentrations of DCNA or DCNA plus captan required for Monilinia decay control, suggested by preliminary laboratory tests on fruit, were verified by these commercial-size experiments.     

EVALUATION OF INSTRUMENTAL METHODS FOR FIRMNESS MEASUREMENT OF FRESH AND CANNED CLINGSTONE PEACHES

The firmness of fresh and canned clingstone peaches was investigated using blade extrusion, back extrusion, and shear-compression instruments. The three techniques yielded results which correlated well among themselves and to sensory evaluation of peach firmness. Results indicate that high vacuum flame sterilization yields a canned product which is closer in firmness to fresh peaches than is the conventionally retorted product.     

IRRADIATION AS AN ALTERNATIVE TO METHYL BROMIDE FOR QUARANTINE TREATMENT OF STONE FRUITS1

Irradiation can be used with cherries, apricots, or peaches as a quarantine treatment at 300gy's or less with little quality loss. Either irradiation or methyl bromide (MeBr) can be used as a quarantine treatment for ‘Bing’‘and ‘Rainier’ sweet cherries with acceptable results and similar fruit quality. Difference in stem condition and bruising were more evident for irradiated ‘Rainier’ cherries than for MeBr treated ‘Rainier’ cherries, but these differences were small. Use of irradiation results in some firmness loss, for ‘Bing’ cherries when compared with MeBr, but irradiation treatment of cherries does not result in a loss of fruit and stem color, where the use of MeBr doses result in both fruit and stem color loss. Apricots (‘Perfection’ and ‘Rival’) and peaches (‘Regina’) are tolerant to irradiation at 300 gy with little quality loss. Loss of firmness, color changes and increased internal breakdown are evident in both apricots and peaches at irradiation dose above 600 gy. If irradiation dose above 600 gy is required to meet quarantine requirements unacceptable qualidy loss will occur in cherries, apricots and peaches.     

PILOT PLANT FOR OSMOTIC DEHYDRATION OF FRUITS: DESIGN AND EVALUATION

This work proposes a pilot scale equipment for osmotic dehydration (OD) of apple cubes that consists of a novel agitation‐immersion device, a bag filter and a vacuum evaporator to conduct simultaneously the OD process, filtration and reconcentration of the osmotic solution (OS). The functional method analysis was used to design the pilot plant. Apple cubes (～1 cm³) were dehydrated using a 60 ° Brix sucrose syrup OS at 50C and a syrup/fruit ratio of 5. OD was conducted either with or without reconcentration of the OS. During the OD process particles of fruit were eliminated from the OS by filtration and the OS concentration was kept at 60 ° Brix by reconcentration in the evaporator. A comparison of the dehydration parameters of apple cubes obtained at pilot scale to those obtained at laboratory scale was done to evaluate the performance of the pilot equipment. The results show that the proposed set‐up can be suitable for commercial production of osmodehydrated fruits.     

USE OF FLEXIBLE POLYMER MATERIAL FOR PACKAGING FRESH PEACHES

Fresh peaches (Prunus persica) were overwrapped in trays with 1 of 3 formulations of flexible polyvinyl chloride (PVC) film that differed in gas transmission rate or they were held in nonwrapped trays (controls). The CO₂ transmission rate at 0°C for PVC type III film was 280 mL/m^2. h (1 atmos); that of type II was 4 times greater and that of type I, about 5 times greater. The peaches were stored either 14 days at 0° or 7.5°C, or 7 days each at 0° and 7.5°C plus 2 days at 20°C to simulate retail display. The mean CO₂ levels were 10, 7.2 and 4.7% in packages that were wrapped with PVC III film and held at 7.5°, 0°/7.5° and 0°C, respectively. CO₂ in packages wrapped with PVC I or II was below 3% at each storage temperature. O₂ concentration remained about 4% in all packages. Weight loss was less and fruit was firmer among those packaged in PVC III than among nonwrapped controls at each of the 3 storage temperatures. Storage temperature had no effect on weight loss or of fruit held in PVC III film. External appearance of fruit packaged with the 3 types of film was significantly better than that of the controls. Internal appearance of the peaches was unaffected by any of the treatments. A microatmosphere favorable for fresh peaches can be maintained within packages overwrapped with polymer films that are selectively permeable to respiratory gases.     

干爽涤纶织物透气透湿性能测试与分析

通过对26种干爽(导湿快干)涤纶织物透气性、透湿性能的测试分析,可以看出:影响织物透气性的主要因素是纱线的组成和织物的紧度。纯涤纶织物,不论其截面形状如何,透气性都差,涤、棉交织物中,涤纶含量越高,透气性越差;纱线越粗,织物的经纬向密度越大,织物的紧度越大,透气性越差;织物的透湿性能与组成纱线纤维的种类,纱线的粗细及经纬纱的密度有关。棉的含量越高,透湿性越好,五叶涤纶丝Coolfibre(CF)与棉交织的织物的透湿能力要优于涤纶DTY与棉交织的织物。     

果蔬酶促褐变机理及其抑制方法研究进展

酶促褐变是果蔬深加工过程中存在的一个普遍且很严重的问题.本文介绍了酶促褐变的基本原理、影响因素,并从物理、化学、生物技术等方面介绍了一些酶促褐变的抑制方法.     

双孢蘑菇的冷冻干燥与高真空干燥

用冷冻干燥法和高真空干燥法分别对双孢蘑菇进行干燥,所得干制品在感官质量和复水性上无明显差别,但是,制品达到相同水分含量所需的干燥时间却有较大差别,高真空干燥法所需时间较短．实验证明,高真空干燥法非常适宜于多孔多纤维类物料（如蔬菜类产品）的干燥,并可在质量不受影响的前提下提高干燥效率．     

AN EXPERIMENTAL STUDY OF MOISTURE AND TEMPERATURE DISTRIBUTIONS DURING FREEZE-DRYING

SUMMARY– Measurements of the moisture and temperature distributions were made during freeze-drying beef at a pressure of 1 torr. The transient moisture distributions measured with gamma ray techniques indicate that the phase change region would have a thickness less than 3/16 in., that no drying takes place until the phase change region reaches a given position, and that no additional drying occurs after the phase change passes a given position. A careful study of the data showed that the drying rate was influenced by heat transfer through the frozen region to the phase change position.