Nutritive value of corn silage as affected by maturity and mechanical processing: a contemporary review

Stage of maturity at harvest and mechanical processing affect the nutritive value of corn silage. The change in nutritive value of corn silage as maturity advances can be measured by animal digestion and macro in situ degradation studies among other methods. Predictive equations using climatic data, vitreousness of corn grain in corn silage, starch reactivity, gelatinization enthalpy, dry matter (DM) of corn grain in corn silage, and DM of corn silage can be used to estimate starch digestibility of corn silage. Whole plant corn silage can be mechanically processed either pre- or postensiling with a kernel processor mounted on a forage harvester, a recutter screen on a forage harvester, or a stationary roller mill. Mechanical processing of corn silage can improve ensiling characteristics, reduce DM losses during ensiling, and improve starch and fiber digestion as a result of fracturing the corn kernels and crushing and shearing the stover and cobs. Improvements in milk production have ranged from 0.2 to 2.0 kg/d when cows were fed mechanically processed corn silage. A consistent improvement in milk protein yield has also been observed when mechanically processed corn silage has been fed. With the advent of mechanical processors, alternative strategies are evident for corn silage management, such as a longer harvest window.     

EFFECT OF PROCESSING PARAMETERS ON THE TEMPERATURE AND MOISTURE CONTENT OF MICROWAVE-BLANCHED PEANUTS

Peanut blanching consists of heat application followed by abrasive removal of the seed coat. The use of a continuous microwave system for the blanching of peanuts has been proposed as a means of reducing processing time and energy costs compared to the traditional hot‐air, multizone oven. The purpose of this research was to characterize effective processing parameters for microwave blanching. The factors examined were the time of exposure in the microwave, use of increased airflow in the microwave applicator during processing and the initial moisture content (MC) of the peanuts. Processing treatments were differentiated by energy absorbed during processing, average and maximum internal temperature, loss in MC and blanchability. High blanchability resulted from higher process temperatures and greater loss in MC. Treatments exceeding 110C resulting in a final MC of 5.5% or below yielded blanchability percentages greater than the 85% industry standard. The time required to generate sufficient heat to dry peanuts for acceptable blanchability is greatly reduced by the use of microwave technology.     

Time and Temperature Parameters of Corn Popping

High quality commercial popcorn containing 14.0% moisture was processed in a continuous hot air domestic corn popper. The time required to pop individual kernels ranged from 35 − 120 sec, with 43% of the corn being cooked between 60 and 75 sec. The temperature of the popping chamber ranged from 196 − 277°C. The average temperature at the center of the kernels when they burst was 187°C. The empirical parameters, f and j values for heat transfer were determined.     

Enzymatic production of pentoses from the hemicellulose fraction of corn residues

Three commercial xylanase preparations were evaluated as a sole enzyme source for the enzymatic production of pentoses from the hemicellulose fraction of corn husks and corn cobs. The hemicellulose fraction was obtained by extracting corn husks or corn cobs with 1.25 mol/l NaOH, and the alkaline extract was used as a substrate for enzymatic hydrolysis. Rapidase Pomaliq (Gist-brocades) was found to yield significantly more pentoses from corn husks and corn conb than Clarex ML (Genenor) or Validase × (Valley Research). Rapidase Pomaliq was capable of increasing the concentration of pentoses from an initial value of 106.5 to 210.6 g/kg dry matter of corn husks or 8.6 to 141.6 g/kg dry matter of corn cobs, respectively, under favorable conditions (480 min of reaction at pH 5.0 and 50 °C). Products of the enzymatic reaction were identified as arabinose, xylose, xylobiose, and xylotriose. The results of this study indicate that Rapidase Pomaliq, an enzyme preparation derived from Aspergillus niger and Trichoderma reesei, could serve as a sole enzyme source for the production of pentoses and xylooligosaccharides from corn residues.     

不同预处理对甜玉米粒干燥品质的影响

采用漂烫和3%盐水浸渍预处理,研究真空冷冻干燥、高真空干燥和真空微波干燥3种不同的干燥方式对玉米干燥品质的影响。通过对硬度、脆度、色泽和感官评分等指标的综合分析,表明2种预处理方式均能改善甜玉米粒干燥品质,对高真空干燥影响最显著,其中浸渍预处理产品的品质优于漂烫预处理,但延长了干燥时间。     

不同热处理过程中鲜食甜玉米类胡萝卜素含量变化研究

为研究加工热处理对鲜食甜玉米中主要类胡萝卜素组分的影响,以晶甜5号鲜食甜玉米为原料,采用高效液相色谱法分析速冻甜玉米烫漂条件、罐装甜玉米预煮和灭菌时间对甜玉米中常见类胡萝卜素变化的影响。结果表明：速冻甜玉米烫漂处理相同时间,蒸汽烫漂甜玉米籽粒中类胡萝卜素含量高于沸水烫漂,且随着烫漂时间的增加,类胡萝卜素的含量在两种烫漂方式下均逐渐下降。对于罐装甜玉米,在20 min内,预煮时间越短总类胡萝卜素含量越高,随着预煮时间增加,仅α-隐黄质含量有所增加,其余均逐渐下降,但预煮时间超过20 min后,总类胡萝卜素含量无明显变化;在10 min内,灭菌处理可以显著提高总类胡萝卜素含量,随着灭菌时间的增加,总类胡萝卜素含量、各种类胡萝卜素组分含量均呈下降趋势。     

Corn silage management I: effects of hybrid,maturity, and mechanical processing on chemical and physical characteristics

Two experiments were conducted to evaluate the effects of hybrid, maturity, and mechanical processing of whole plant corn on chemical and physical characteristics, particle size, pack density, and dry matter recovery. In the first experiment, hybrid 3845 whole plant corn was harvested at hard dough, one-third milkline, and two-thirds milkline with a theoretical length-of-cut of 6.4 mm. In the second experiment, hybrids 3845 and Quanta were harvested at one-third milkline, two-thirds milkline, and blackline stages of maturity with a theoretical length-of-cut of 12.7 mm. At each stage of maturity, corn was harvested with and without mechanical processing by using a John Deere 5830 harvester with an onboard kernel processor. The percentage of intact corn kernels present in unprocessed corn silage explained 62% of variation in total tract starch digestibility. As the amount of intact kernels increased, total tract starch digestibility decreased. Post-ensiled vitreousness of corn kernels within the corn silage explained 31 and 48% of the variation of total tract starch digestibility for processed and unprocessed treatments, respectively. For a given amount of vitreous starch in corn kernels, total tract starch digestibility was lower for cows fed unprocessed corn silage compared with processed corn silage. This suggests that processing corn silage disrupts the dense protein matrix within the corn kernel where starch is embedded, therefore making the starch more available for digestion. Particle size of corn silage and orts that contained corn silage was reduced when it was processed. Wet pack density was greater for processed compared with unprocessed corn silage.     

Influence of process and product variables on extrusion energy and pressure requirements

Energy and pressure requirements for processing foods as affected by product moisture content and extruder barrel temperature and screw speed were studied using corn gluten meal (CGM) processed in a C.W. Brabender laboratory single-screw cooker-extruder. The extruder screw was 1·9 cm in diameter, had a 3:1 compression ratio and a 20:1 barrel length-to-diameter ratio. The die-end nozzle was 3 mm in diameter. Moisture contents were 14, 20 and 26% (dry basis), extruder barrel temperatures were 120, 145 and 170°C and the extruder screw speeds were 100, 150 and 200 rpm. Regression analysis showed that moisture content contributed most to the variation in energy requirements (32·4%), followed by temperature (12·4%). Effect of screw speed was found to be insignificant. Increasing moisture content and barrel temperature caused specific energy to decrease. Pressure was found to be significantly affected and decreased with increases in all three variables.     

Influence of drying and hydrothermal treatment of corn on the denaturation of salt-soluble proteins and color parameters

The effect of heat treatments (drying and hydrothermal treatment) on the extractability of salt-soluble protein (SSP) was assessed using Promatest methodology for corn kernels heated between 60 °C and 120 °C. During drying, the evolution of the grain moisture content is fitted using the analytical solution of Fick equation developed by Crank (1979) for spherical material. The decrease of extractible salt-soluble protein during heating is forecasted using a first and a second order ordinary differential equation. It was found that temperature; moisture content and time of processing greatly influence the kinetic denaturation of SSP of corn kernels. The evolution of extractible SSP content of corn kernels during drying at high temperature is more correctly described with second order kinetic than with the first order kinetic reaction. The Hunterlab color parameters of corn also vary during drying. Lightness and color intensity decrease while yellowness, redness, chroma and hue angle increase through drying time. Most of these Hunterlab color parameters are highly correlated with the salt-soluble proteins content and therefore could be used as indicators of excessive heat treatment and denaturation of salt-soluble proteins in corn kernels.     

热泵式长豇豆干燥工艺优化

为保证热泵干燥后长豇豆产品的复水性和色泽等品质参数良好,同时降低豇豆干燥过程中的能量消耗,提高豇豆干燥生产的效率,采用Box-Behnken试验设计,分析干燥温度、漂烫时间和铺料密度3 个因素对豇豆产品的复水率、色差、单位耗能量和耗时4 个参数的影响,建立多元回归模型,并对干燥工艺参数进行优化,得到热泵式长豇豆干燥工艺的最佳条件为漂烫时间3 min、铺料密度2 kg/m2、干燥温度50 ℃。在该工艺条件下,实际测得长豇豆复水率1.15,色差值22.39,单位耗能量14.31（kW·h）/kg,耗时7 h,与预测值误差极小,为豇豆在实际热泵式干燥设备生产加工中的应用提供一定的理论依据。     

Clean label starches as thickeners in white sauces. Shearing, heating and freeze/thaw stability

The linear viscoelastic properties and syneresis of freshly prepared and freeze/thawed white sauces prepared with different native starches (corn, waxy corn, potato and rice) at different shearing speeds were studied. Viscosity changes during processing were also measured using a starch pasting cell attached to a rheometer. The freeze/thaw cycle produced a significant increase in the viscous and elastic modulus and the appearance of syneresis in the corn and potato starch sauces, while the waxy corn and rice starch sauces were only slightly affected. Syneresis was significantly reduced upon subsequent heating. Greater shearing speed produced a significant decrease in viscoelasticity. Viscosity profiles revealed that the increase in shearing speed decreased the starch gelatinization temperature and swelling capacity and increased starch breakdown.     

Water changes in canned dry peas and beans during heat processing

The amount of water absorbed by dry peas ( Pissum sativum L. cv. 'Marrowfat') and dry beans ( Phaseolus vulgaris L. cv. 'Haricot') during soaking, blanching and canning was studied. The temperature during soaking significantly affected the water absorption rate up to 40 °C, but not beyond this temperature. The final water content of the product was significantly increased by blanching after soaking as opposed to blanching before soaking. Water uptake was also significantly affected by the water used. Total water uptake was about 150% greater in peas when soft water was used (60 °C). High soaking temperatures with correspondingly short soaking time (4 h at 60 °C) would be advantageous to a food manufacturer. Under these conditions, water absorption is increased in the finished product and the amount of product 'in process' is reduced, allowing a greater flexibility and control of the process.     

Canned Dry Bean Quality as Influenced by High Temperature Short Time (HIST) Steam Blanching

High temperature short time (HTST) steam blanched dry beans had greater drained weights and shear values than water blanched dry beans. Moisture content of dry beans was greater after water blanching. Subjective grade was closely related to drained weights and shear values, and HTST steam blanched dry beans had better subjective grades than water blanched dry beans. Water blanched dry beans were lighter in color than HTST steam blanched dry beans. As length of HTST steam blanch was increased, Agtron color of the beans darkened. High quality canned dry beans can be produced with HTST steam blanching with energy and time savings, but differences between water and HTST steam blanching and canning quality is highly dependent on cultivar and length of HTST steam blanch.     

冷藏调理即食鲨鱼皮增脆工艺研究

本文以鲨鱼皮为原料,研究冷藏调理即食鲨鱼皮的增脆工艺技术。在单因素基础上采用三因素二次通用旋转回归试验设计方案,以产品的剪切力为衡量指标,建立了冷藏调理即食鲨鱼皮剪切力Y与六偏磷酸钠溶液的浓度X1、漂烫时间X2与冰水急冷时间X3的数学回归模型,并对三因子的最优组合进行了定量探讨。结果表明,冷藏调理即食鲨鱼皮增脆的最佳工艺参数组合为:六偏磷酸钠溶液浓度4.0g·L-1,漂烫时间2.0min,冰水急冷时间13min,在此条件下制备的冷藏调理即食鲨鱼皮产品剪切力为26.52N,口感良好。     

甜玉米粒烫漂护色技术研究

对甜玉米粒烫漂护色条件进行了研究。结果表明:以0.08%NaCl+0.03%VC+0.06%柠檬酸配制护色液,进行护色处理,护色效果佳。烫漂温度在90℃,时间为10min,料水比为1∶4.5时能最大限度地保证其品质。过氧化物酶活性与烫漂时间关系最大,其次是烫漂温度,与料水比的关系不显著。     

Osmotic dehydration process for low temperature blanched pumpkin

This study investigated the influence of stepwise blanching over the kinetics of osmotic dehydration process and over the physical characteristics of pumpkin (Cucurbita moschata). The 2³ factorial design and response surface methodology was used to optimize the blanching process. The independent variables for blanching were temperature, blanching time and holding time. These independent variables showed different effects on the two studied answers: texture and color. The kinetics of osmotic dehydration were investigated using 50% and 65% sucrose solutions, using samples previously blanched by both stepwise and conventional means. The diffusivity values for the water and sucrose were similar for the two components, showing greater gains of solute than loss of water in many samples. Blanching affected the color of the pumpkin, whereas osmotic dehydration did not change it significantly. The impregnation process maintained or even increased the tissue firmness when compared to the blanched samples.     

A novel method of shrimp blanching by CO2 heat pump: Quality,energy, and economy analysis

To reduce the energy consumption of the shrimp blanching process and improve the economic value of the blanched product, a transcritical CO₂ heat pump blanching system (THPB system) was designed in this paper. The trends of astaxanthin were investigated at atmospheric pressure near boiling temperature, combined with the color and structural properties of shrimp samples, and the optimal blanching times of 270 s and 240 s were obtained at 90°C and 95°C, respectively. In contrast to the fuel blanching system (FB system) at 100°C, the annual standard coal consumption of the THPB system with 90°C blanching is decreased by 79%, and the annual operating cost can be saved by CNY 63,800, with a payback period of about 3.13 years.Industrial relevanceBlanching is one of the effective ways to prolong the shelf life of shrimp. However, the research on the blanching time and temperature of shrimp is not comprehensive. In addition, the traditional fuel blanching process has high energy consumption and pollution, and can no longer meet the quality requirements of the modern food processing industry. Heat pump has been shown to have better performance in food drying, but it is less used in blanching. The information presented in this study may provide other insights into food processing.     

Occurrence of Aspergillus spp. and aflatoxins in commercial mushroom compost

One hundred and thirty-three isolates of Aspergillus spp. were collected from commercial mushroom houses. Aflatoxins were detected in three samples of compost. Seventy-three per cent of the isolates produced aflatoxins in liquid media. Aflatoxins were produced on sterilized and pasteurized compost plus the components of compost including rye grain, corn cobs and commercial spawn; 24°C was a more favourable temperature for aflatoxins than 14°C. Aflatoxin production varied with isolate, substrate and temperature and ranged from no aflatoxins to all four aflatoxins B1, B2, GI and G1.     

Flavour Qualities of Frozen Sweetcorn are Affected by Genotype and Blanching

Peroxidase activity is used by the food processing industry as an indicator of adequacy of the blanching process and to predict off-flavour development in frozen food. Research reported herein showed that total peroxidase activity did not parallel flavour changes in frozen unblanched supersweet (sh2) or sugary enhanced (su1/se) sweet corn genotypes. Frozen corn-on-the-cob of ‘Florida Staysweet’ (sh2), ‘Merit’ (standard sweet—su1) and ‘Bodacious’ (su1/se), blanched and unblanched, was subjected to sensory evaluation and peroxidase analysis following frozen storage up to 12 months. Trained taste panellists rated the unblanched sh2 and su1/se corn as acceptable up to 8 months of frozen storage. Kernels were cut from cobs after 0 and 12 months of storage. Proteins were extracted from acetone powders of kernels and separated by isoelectric focusing and native PAGE. Banding patterns differed according to genotype and storage duration. These results suggested molecular differences in peroxidase isozymes among the sweet corn genotypes which could be involved in off-flavour development. All genotypes contained a peroxidase isozyme having a molecular mass of 80 kDa and pI of 4·5. The su1/se and sh2 genotypes produced an additional peroxidase band of 13·8 kDa. An additional peroxidase isozyme (pI 5·4) appeared in extracts from the su1 genotype after 12 months storage. Although changes in total peroxidase activity may not predict flavour changes in all genotypes, the presence or absence of certain peroxidase isozymes may be useful in predicting off-flavour development in su1 frozen corn.     

不同浓度NaCl处理对发芽玉米中类胡萝卜素富集的影响

本文旨在研究不同浓度NaCl处理对发芽玉米籽粒中类胡萝卜素富集、抗氧化能力及其合成途径中关键酶基因表达量的影响。结果表明,NaCl胁迫下,发芽3 d玉米籽粒的发芽率和芽长显著下降,呼吸强度显著增加。随NaCl浓度升高,发芽玉米籽粒中类胡萝卜素含量及其合成途径中关键酶基因表达量先上升后下降,300 mmol/L NaCl处理下均达到最大值,其中叶黄素和玉米黄质含量分别为对照的1.19和1.30倍。同时,其超氧化物歧化酶、过氧化物酶活性及总抗氧化能力显著增加。NaCl浓度大于300mmo/L时,关键酶基因相对表达量均下降,类胡萝卜素的合成被抑制。NaCl处理可提高类胡萝卜素合成相关酶基因表达量,促进叶黄素、玉米黄质等类胡萝卜素富集,同时其抗氧化能力有所提高。研究结果为玉米籽粒富集类胡萝卜素开创了新思路,并为开发玉米籽粒保健功能食品提供理论依据和技术支撑。