Precipitation of cheddar cheese whey lipids by electrochemical acidification

Lipid separation from cheddar cheese whey allows a better valorization of protein fractions. In this study, bipolar membrane electroacidification (BMEA) was used to obtain precipitates with a high level of lipids. Whey samples with normal and low (by way of electrodialysis) mineral salt levels have been treated by a BMEA process and centrifuged. The composition of flocs and precipitation yields were determined. The BMEA process increased lipid precipitation rates by almost 50% in comparison with a centrifugation step only whereas a demineralization step prior to electroacidification had a limited effect on the precipitation level. Precipitates obtained were mainly composed of lipids (probably phospholipids) but also contained proteins. BMEA of cheddar cheese whey would allow the production of a lipid-enriched fraction and of a protein-enriched whey.     

Starter bacteria are the prime agents of lipolysis in cheddar cheese

To assess the contribution of starter lactic acid bacteria (LAB) to lipolysis in Cheddar cheese, the evolution of free fatty acids (FFAs) was monitored in Cheddar cheeses manufactured from pasteurized milks with or without starter. Starter-free cheeses were acidified by a combination of lactic acid and glucono-delta-lactone. Starter cultures were found to actively produce FFAs in the cheese vat, and mean levels of FFAs were significantly higher in starter cheeses over ripening. The contribution of nonstarter LAB toward lipolysis appears minimal, especially in starter-acidified cheeses. It is postulated that the moderate increases in FFAs in Cheddar cheese are primarily due to lack of access of esterase of LAB to suitable lipid substrate. The results of this study indicate that starter esterases are the primary contributors to lipolysis in Cheddar cheese made from good quality pasteurized milk.     

Antioxidant properties of green tea extract protect reduced fat soft cheese against oxidation induced by light exposure

The effect of two different antioxidants, EDTA and green tea extract (GTE), used individually or in combination, on the light-induced oxidation of reduced fat soft cheeses (0.2 and 6% fat) was investigated. In samples with 0.2% fat, lipid hydroperoxides as primary lipid oxidation products were not detected, but their interference was suggested from the formation of secondary lipid oxidation products such as hexanal and heptanal. The occurrence of these oxidation markers was inhibited by spiking with 50 ppm EDTA or 750 ppm GTE, or a combination of the two prior to irradiation. In contrast, addition of 50 ppm EDTA to samples with 6% fat was ineffective, but 750 ppm GTE (alone or in combination with EDTA) strongly reduced levels of hexanal and heptanal. Accumulation of primary lipid hydroperoxides was not affected by GTE, hence antioxidative activity was ascribed to scavenging of hexanal and heptanal precursors. These radical intermediates result from hydroperoxide disintegration, and subsequent scavenging by GTE, which acts as a radical sink, corroborates the intense signal observed by electron paramagnetic resonance (EPR) spectroscopy.     

Influence of a probiotic adjunct culture of Enterococcus faecium on the quality of cheddar cheese

Cheddar cheese has previously been shown to be an effective vehicle for delivery of viable cells of a probiotic Enterococcus faecium strain to the gastrointestinal tract. The particular strain, E. faecium PR88, has proven efficacy in the treatment of irritable bowel syndrome, and in this study it was evaluated for suitability as a starter adjunct for Cheddar cheese manufacture. When added to cheesemilk at an inoculum of 2 x 10(7) cfu/mL, the enterococcal adjunct maintained viability in Cheddar cheese at levels of up to 3 x 10(8) cfu/g during 9 months of ripening. Increased proteolysis and higher levels of some odor-active volatile compounds were observed in Cheddar cheeses containing the PR88 adjunct compared with the control throughout the ripening period. In addition, the enterococcal adjunct strain did not affect cheese composition. Although sensory evaluation showed no significant difference in flavor/aroma and body/texture scores between control and experimental cheeses, repeated comments by the commercial grader consistently described the cheeses containing PR88 as 'more advanced than the control' and as having 'better flavor'. These findings indicate that the presence of the PR88 adjunct strain in Cheddar cheese at levels of >/=10(8) cfu/g may positively influence Cheddar flavor.     

Accelerated extraction of the fat content in cheese using a focused microwave-assisted soxhlet device

A fast method for hydrolysis and extraction of fat in cheese based on the use of a Soxhlet extractor assisted by microwaves is proposed. The use of this type of energy dramatically reduces the time required for both steps (namely, the hydrolysis time was decreased from 1 h to 10 min with avoidance of the neutralization step, and the extraction time was decreased from 6 h to 40 min), providing similar efficiency and reproducibility comparable to or better than that of the conventional Soxhlet methodology. In addition, the proposed method is cleaner than conventional Soxhlet, as 80-85% of the extractant is recycled. The determination of the fatty acid composition by gas-liquid chromatography and quantification of both polymer formation by high-performance size exclusion liquid chromatography and nonpolar triacylglycerol formation by thin-layer chromatography with flame ionization detection in the extracts obtained by the proposed method, conventional Soxhlet and Weibull-Berntrop procedures (Soxhlet with a prior hydrolysis step), showed that the quality of the extracts obtained by the proposed procedure is better than that of the conventional alternatives, possibly due to the shorter time required by the accelerated method.     

Flavor enhancement of chicken broth from boiled celery constituents

The flavor-enhancing effects of the volatile constituents in celery were investigated. The test samples were prepared by adding celery fractions to chicken broth at a concentration that distinct odors of them were not detected, and the samples were sensorially evaluated for the perceived intensities of 8 terms such as "thick," "impactful," "mild," "lasting," "satisfied," "complex," "refined," and "clarified," which are considered to be the elements of the complex flavor and for 3 terms such as "sweet," "salty," and "umami" taste. A comparison of effects between the volatile and nonvolatile fractions of celery revealed that the volatile compounds in celery enhanced the complex flavor of chicken broth more than the nonvolatile compounds. Among the characteristic odorants of celery, three phthalides, namely, sedanenolide, 3- n-butylphthalide, and sedanolide, were shown to contribute to the complex flavor of chicken broth, and sedanenolide was most effective. The three phthalides enhanced perceived intensities of "umami" and "sweet" despite their no taste properties in addition to the complex flavor.     

Quantification of beta casein in milk and cheese using an optical immunosensor

beta-Casein was quantified in milk and cheese, using an optical immunosensor, based on surface plasmon resonance (SPR) measurement. The assay consists of a two-step sandwich strategy, with two anti-beta-casein antibodies directed against each extremity of the casein. This strategy permits only native beta-casein to be quantified and not its degradation products. The calibration curve was obtained with a reference milk powder of known beta-casein concentration. The analysis time per sample was less than 10 minutes. The antibody-coated surface could be used for more than 250 determinations. The detection limit was established at 85 ng x mL(-)(1) and the intra- and inter-assay variation coefficients were 2.6 and 6.2% respectively. The method was applied to raw milk to quantify intact beta-casein, with no pretreatment of the sample. A second application was realized with cheese, to follow the proteolysis of beta-casein during ripening.     

Relationship between MALDI-TOF analysis of beta-CN f193-209 concentration and sensory evaluation of bitterness intensity of aged cheddar cheese

An internal standard method was previously developed to measure the concentration of a synthetic bitter peptide, beta-CN f193-209, by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The objective of this study was to evaluate the relationship between beta-CN f193-209 concentration in an aqueous extract of aged Cheddar cheese and bitterness intensity of the cheese. Concentrations of beta-CN f193-209 in cheese extracts were determined by MALDI-TOF at 0, 120, 180, and 270 days. Trained panels evaluated the bitterness intensity of the cheeses at 180 and 270 days. Correlation coefficients between MALDI and sensory data at 180 and 270 days were 0.803 and 0.554, respectively. The decreased correlation may be due to the presence of other bitter peptides more responsible for bitterness at longer aging or the production of compounds that mask bitterness intensity.     

Modified atmosphere packaged cheddar cheese shreds: influence of fluorescent light exposure and gas type on color and production of volatile compounds

The influences of fluorescent light exposure and packaging atmosphere on the headspace volatiles and color of Cheddar cheese shreds were evaluated using gas chromatography-mass spectrometry and spectrocolorimetry, respectively. Cheddar cheeses were packaged under atmospheres of 100% carbon dioxide or 100% nitrogen and stored at 4 degrees C under fluorescent light for 6 weeks. Cheeses stored under carbon dioxide contained higher concentrations of aldehydes and fatty acids and lower concentrations of alcohols and esters than cheeses stored under nitrogen. Carbon dioxide atmospheres potentiated light-induced oxidation in shredded Cheddar cheeses, as evidenced by aldehyde and fatty acid headspace volatiles measured following storage. Color bleaching occurred only in cheeses packaged under carbon dioxide and exposed to light. The shift in color is proposed to be due to an interaction between carbon dioxide and high-intensity light, leading to the oxidation of the pigment molecule, bixin. The results have significant implications for procedures used to handle and store pigmented cheeses to ensure desirable flavor and consumer acceptability.     

Lipolysis during ripening of Emmental cheese considering organization of fat and preferential localization of bacteria

This study followed the progression of lipolysis in Emmental cheese by quantifying the concentrations of individual free fatty acids (FFA) released during ripening in each of the different rooms: 12 days at 12 degrees C, 28 days at 21 degrees C, and 8 days at 4 degrees C. Lipolysis, which corresponded to 1.56% of fat, mainly occurred in the 21 and 4 degrees C rooms, with 68 and 16.5% of total FFA, respectively. The nonselectivity of lipolytic enzymes was evidenced: all fatty acids were released with level of > or =1%. Differential scanning calorimetry experiments showed that the thermal properties of cheese were affected by (i) lipolysis of fat, that is, the monoacylglycerols, diacylglycerols, and FFA that may be localized at the fat/whey interface, and/or by (ii) hydrolysis of high-melting-point triacylglycerols constituted mainly by long-chain saturated fatty acids (e.g., palmitic acid). Analysis of the cheese microstructure was performed using confocal laser scanning microscopy. Fat globules were mainly disrupted after pressing of curd grains, leading to the release of the milk fat globule membrane (MFGM); fat inclusions were surrounded by pockets of whey, delimited by casein strands. Moreover, colonies of bacteria were preferentially localized in situ at the fat/protein interface. This study showed that both the localization of bacteria and the supramolecular organization of fat which was not protected by the MFGM can help the accessibility of milk fat to lipolytic enzymes and then contribute to the quality of cheese.     

基于指标体系的河北省农业循环经济发展评价

在农业循环经济内涵基础上,构建了农业循环经济发展水平的综合评价指标体系,指标体系包括经济与社会发展、资源减量化投入、资源循环再利用及资源环境安全等4个类指标共18个操作化指标.并对河北省1991～2005年农业循环经济发展水平进行评价.结果表明,河北省农业循环经济整体水平逐年上升,主要是由于农业产出水平提高的拉动;农业投入水平是最主要制约因素;资源循环再利用水平多年徘徊不前;农业资源环境安全基本得到了保障.     

Straightforward process for removal of milk fat globule membranes and production of fat-free whey protein concentrate from cheese whey

A straightforward method for the separation of milk fat globule membrane (MFGM) and production of fat-free whey protein concentrate/isolate from cheese whey has been developed. Lowering of the conductivity of the whey from its initial value of about 5600 μS cm(-1) to about 2000-500 μS cm(-1) via diafiltration with water caused selective precipitation of MFGM when incubated for 30 min at pH 4.2 and 35 °C. The whey proteins remained soluble in the supernatant under these conditions. Experimental evidence suggested that precipitation of MFGM at pH 4.2 was not due to a nonspecific effect of lowering of the conductivity of the whey but due to the specific effect of removal of Ca2+ from the whey. The lipid content of whey protein isolate obtained by this process was <0.2%, and the protein loss was <14%. The method provides an industrially feasible process for the production of fat-free whey protein concentrate/isolate. The MFGM, which is reported to contain bioactive/nutraceutical lipids and proteins, is a valuable byproduct of the process.     

Soil surface drip point features: an integrated approach using analytical photogrammetry and soil micromorphology

This study considers changes occurring on a soil surface after exposure to simulated rainfall. The soil surface in question has a crop cover of artificial maize, and interest focuses specifically on the surface features produced by leaf drips. An analytical photogrammetric approach is used to examine surface morphological change at a small scale (1 mm). These topographical changes are then related to sub-surface crust development as observed by the use of impregnated polished blocks. For the first time therefore soil surface and soil sub-surface changes are integrated together in one study. The results reveal a ‘cut and fill' type process in which aggregate welding and breakdown operate in parallel.     

基于小波变换的农业图像增强方法研究

国内外有关果品、植物、昆虫等农业图像处理大都采用常规的方法，这些方法要么仅在时域要么仅在频域，而不能同时在时域和频域分析图像，且不具有多分辨率特性。该研究应用小波变换这一新理论、新方法，深入开展农业图像增强方面的研究工作。将小波变换应用于低对比度的仙客来图像、橙子剖面图的增强，设计了加强低频弱化高频、增强低频合并原图像两种算法，解决了传统的直方图均值化、对数变换以及LoG Filter等方法不能较好地使图像增强的问题；又将小波变换应用于含有皱褶及裂纹的红枣图像的增强，通过加强高频弱化低频，很方便地使得红枣的裂纹和皱褶更加明显，便于分级与检测。结果表明基于小波变换的农业图像增强算法方便简捷、效果良好。     

整建制全要素全链条农业面源污染综合防治的思考及实践

加强农业面源污染综合防治是加快推进中国农业发展全面绿色转型,实现乡村全面振兴的重要任务。近年来,在多方的共同努力下,中国生态环境改善取得了一定成效,但重点流域的农业面源污染问题仍然突出。该研究在分析中国农业面源污染现状的基础上,通过资料收集、现场调研、专家座谈等多种方式梳理和分析了农业面源污染综合防治在治理主体、投入要素、技术体系与产业链条方面的瓶颈,解析了整建制全要素全链条农业面源污染综合防治的内涵,阐述了国家农业绿色发展先行区浙江平湖在践行整建制全要素全链条农业面源污染综合防治方面的先进做法及应用效果。总结了典型案例在网格化健全污染综合防治“整建制”、特色化延伸综合防治“全链条”、以及全方位保障污染综合防治“全要素”三个方面开展的相关工作,以期为探索形成农业面源污染综合防治整体解决方案,示范带动农业发展全面绿色转型提供支撑。     

Assessing potential bioavailability of raspberry anthocyanins using an in vitro digestion system

The bioavailability of anthocyanins from raspberry extracts was assessed using an in vitro digestion procedure that mimics the physiochemical and biochemical changes that occur in the upper gastrointestinal tract (GIT). Effectively all of the total phenol content of the raspberry extract survived gastric digestion and partitioned between the IN sample, which represents the serum available material, and the OUT sample, which represents the material that remains in the GIT and passes through to the colon. All of the anthocyanins also survived gastric digestion, but only approximately 5% entered the IN sample and approximately 70% of total anthocyanins were recovered in the IN and OUT samples. Codigestion of the raspberry extract with commonly combined foodstuffs such as bread, breakfast cereal, ice cream, and cooked minced beef gave a different pattern. The total phenol content of the IN samples was slightly reduced by codigestion with ice cream or breakfast cereal but unaffected by codigestion with bread or minced beef. In most cases, the phenol contents of the postgastric and OUT samples were reduced as compared with the expected values. However, the anthocyanin content of the IN samples was unaffected or increased by coincubation with the foodstuffs. This suggests that polyphenols transiently bind to food matrices during digestion, which protects the more labile anthocyanins from degradation, and they are free to diffuse into the IN sample. The anthocyanin composition of the bioavailability samples was monitored by liquid chromatography-mass spectrometry. All eight anthocyanins previously identified in raspberry were detected in the extract and the postgastric samples at similar yields. All eight anthocyanins could be discerned in the IN and OUT samples, but some such as cyanidin-3-O-glucoside were greatly reduced and others such as pelargonidin-3-O-glucoside were apparently increased in abundance. These differences in stability and their importance for the bioavailability of anthocyanins are discussed.     

Multiresidue screening of pesticides in fruits using an automatic solid-phase extraction system

About 20 pesticides were determined in lyophilized fruits using a semiautomatic multiresidue method, based on solid-phase extraction (SPE) with a silica column. The lyophilization of the sample, besides the SPE procedure selected, provided clean extracts despite the complexity of the matrixes studied. In addition, the lyophilization process allows sample preservation for at least three months without changes in the concentrations of the pesticides. Determination and quantitation of organochlorine and pyrethroid residues was carried out using a gas chromatograph equipped with an electron capture detector (GC-ECD), and a mass spectrometric detector (GC-MS) was used for confirmation purposes. Organochlorine pesticides provided average recoveries (spiked at three concentration levels in eight different fruits) near 93 +/- 4%, being lower (89 +/- 8%) for pyrethroids as a consequence of their higher degradation and interaction with the sample matrix. On the other hand, the detection limits achieved for all pesticides (0.5-8 ng per g of lyophilized fruit) allow their determination at the MRLs established by the European Union, with good precision ( approximately 5%). Finally, from the 100 different fruits screened, only 10 positive responses were obtained, which were further confirmed by GC-MS.