Aroma analysis of light-exposed milk stored with and without natural and synthetic antioxidants

The effect of antioxidants, added in a single initial dose or in weekly additions to extended shelf life milk, was evaluated over 6 wk of lighted storage at 4 degrees C. Light-induced oxidation was measured by determining pentanal, hexanal, heptanal, and 1-octen-3-ol contents. Weekly addition of a combination of butylated hydroxyanisole and butylated hydroxytoluene (100 mg/kg of milk fat, each) maintained heptanal content of milk at levels comparable to light-protected milk, whereas an initial single addition of alpha-tocopherol significantly decreased hexanal content over the first 4 wk of storage. Odor-active compounds associated with light-induced oxidation included 2,3-butanedione, pentanal, dimethyl disulfide, hexanal, 1-hexanol, heptanal, 1-heptanol, and nonanal. The addition of butylated hydroxyanisole and butylated hydroxytoluene in a single initial addition resulted in decreases in pentanal and hexanal odor, but not in heptanal and 1-heptanol odor, whereas the addition of alpha-tocopherol and ascorbyl palmitate decreased pentanal and heptanol odor, but not hexanal and heptanal odor.     

乳及其制品中风味物质的研究进展

乳尤其是发酵乳中的风味物质种类繁多,包括非挥发性酸、挥发酸、羰基化合物以及蛋白、脂肪和乳糖等的分解物。由于加工过程中微生物和理化的原因,容易使乳制品产生不良风味。通过加入抗氧化剂等添加剂、加强杀菌措施、控制原料奶的品质和环境条件来控制风味的变化,提高其品质。     

Increasing omega fatty acid content in cow's milk through diet manipulation: Effect on milk flavor

Milk with an increased content of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and conjugated linoleic acid (CLA) was obtained by incorporating fish oil into the feed of cows. The 4 feed treatments used were a control diet of 57% forage and 43% concentrate mix with EnerGII fat supplement at 1.65% of dietary DM, or EnerGII in the basal diet was partially replaced with 1) 0.21% partially ruminally inert calcium salts of 71% fish oil given at 0.41% of DM; 2) 0.41% inert calcium salts of 71% fish oil given at 0.83% of DM; or 3) 0.83% inert calcium salts of 43% fish oil given at 0.83% of DM. The cows were milked after 5 and 8 wk and the EPA, DHA, and CLA contents in the pasteurized whole milk were determined. The presence of off-flavors in the milk was investigated after 3 and 10 d of storage. Twelve judges were trained to evaluate the presence of grassy, fishy, oily, oxidized, and rancid off-flavors. Although levels of EPA, DHA, vaccenic acid, and CLA increased for all 4 treatments, a trained sensory panel detected no difference in milk flavor between treatments and the control, with little or no intensity of off-flavors. Results suggest that feeding fish oil and EnerGII at varying levels enhanced CLA, EPA, DHA, and total n-3 fatty acids in milk over the length of the experiment without negatively affecting milk flavor. This creates the potential for a more marketable and healthful product.     

配制型酸乳饮料的稳定性和风味研究

配制型酸乳饮料不仅营养丰富,风味酸甜可口,而且生产工艺相对简单,在市场上很有竞争力。研究配制型酸乳饮料的生产工艺,结果表明:当全脂奶粉含量为5%时,同时添加耐酸CMC0.2%和阿拉伯可尔0.1%两种稳定剂,稳定性很好,口感细腻无异味。进一步添加1.0%的变性淀粉TAX-TRA,可以增加酸乳饮料风味、厚实感明显加强、余味更足。当酸乳饮料pH为4.0时,添加10%蔗糖或6%蔗糖和0.02%安赛蜜都可以使饮料酸甜可口。     

羊奶膻味脂肪酸代谢调控研究

山羊奶是一种营养完全的食品,含有能促进人类生长发育以及维持健康的必需营养成分,它所含各种营养成分的比例,大体适合人类的生理需要。发展山羊奶业不仅是对中国奶业数量上的补充,而且在品质上,与牛奶相比更具潜力。但是由于羊奶具有膻味,因此羊奶及其制品的市场占有率很低。研究证明羊奶中短、中链脂肪酸是造成膻味的主要原因。文章对近年来羊奶膻味与脂肪酸代谢及基因调控等的研究状况进行了综述。     

奶香风味香肠生产加工工艺

介绍奶香风味香肠的基本配方和对生产加工工艺进行研究,奶香风味香肠具有自然浓郁的奶香、营养丰富、风味独特,产品使用方便,卫生安全。     

蒸汽浸入式UHT杀菌对牛乳部分营养物质和口感的影响

以蒸汽喷入式和管式间接加热为对照,利用135℃(4 s)蒸汽浸入式对鲜牛乳进行杀菌试验,对杀菌乳的部分营养性和口感进行了评价。结果表明,3种加热方式都可以满足商业无菌产品要求;其中蒸汽直接浸入式条件下,α-乳白蛋白、乳铁蛋白、维生素B1、维生素B12、维生素C和叶酸的损失率均低于其他两种杀菌方式;蒸汽浸入式杀菌产品中蒸煮味更淡。蒸汽浸入式杀菌方式对牛乳无菌加工过程中的营养保留率更高。     

奶香香精陈化过程中一些化学现象初探

用气相色谱-质谱联用方法对一款自制奶香精新配制时与陈化三月后的成分进行了分析比较,发现并初步解析了其中的几种香原料如酮类、酸类、醛类、内酯类等在陈化过程中发生的一系列化学变化。     

Identification of objectionable flavors in purported spontaneous oxidized flavor bovine milk

Spontaneous oxidized flavor (SOF) has been reported over the past 5 decades as a sporadic objectionable flavor problem in bovine milk. Parameters previously reported to influence SOF development in milk have been contradictory, limiting the ability to monitor and develop mitigation strategies. The current paper investigates the causative compounds associated with milk identified as SOF milk in the Midwest dairy region of the United States. Based on GC/MS-olfactometry analysis, endo-borneol, 2-methylisoborneol, and α-terpineol were identified as the off-flavor compounds. Sensory recombination studies further confirmed the sensory contribution of these compounds to the noted off-flavor attributes in the original milk, which were described as “green,” “musty,” and “unclean.” These compounds are known microbial-derived flavor taints, indicating oxidation was not the origin of the objectionable flavor in the milk. This noted misclassification of the milk as SOF indicates the challenge of defining flavor defects without the identification of the active compounds.     

The effect of vitamin concentrates on the flavor of pasteurized fluid milk

Fluid milk consumption in the United States continues to decline. As a result, the level of dietary vitamin D provided by fluid milk in the United States diet has also declined. Undesirable flavor(s)/off flavor(s) in fluid milk can negatively affect milk consumption and consumer product acceptability. The objectives of this study were to identify aroma-active compounds in vitamin concentrates used to fortify fluid milk, and to determine the influence of vitamin A and D fortification on the flavor of milk. The aroma profiles of 14 commercial vitamin concentrates (vitamins A and D), in both oil-soluble and water-dispersible forms, were evaluated by sensory and instrumental volatile compound analyses. Orthonasal thresholds were determined for 8 key aroma-active compounds in skim and whole milk. Six representative vitamin concentrates were selected to fortify skim and 2% fat pasteurized milks (vitamin A at 1,500–3,000 IU/qt, vitamin D at 200–1,200 IU/qt, vitamin A and D at 1,000/200–6,000/1,200 IU/qt). Pasteurized milks were evaluated by sensory and instrumental volatile compound analyses and by consumers. Fat content, vitamin content, and fat globule particle size were also determined. The entire experiment was done in duplicate. Water-dispersible vitamin concentrates had overall higher aroma intensities and more detected aroma-active compounds than oil-soluble vitamin concentrates. Trained panelists and consumers were able to detect flavor differences between skim milks fortified with water-dispersible vitamin A or vitamin A and D, and unfortified skim milks. Consumers were unable to detect flavor differences in oil-soluble fortified milks, but trained panelists documented a faint carrot flavor in oil-soluble fortified skim milks at higher vitamin A concentrations (3,000–6,000 IU). No differences were detected in skim milks fortified with vitamin D, and no differences were detected in any 2% milk. These results demonstrate that vitamin concentrates may contribute to off flavor(s) in fluid milk, especially in skim milk fortified with water-dispersible vitamin concentrates.     

焙烤对核桃仁风味及其油脂氧化的影响

焙烤可以有效增加坚果的风味,但由于坚果中含有的大量不饱和脂肪酸极易受热氧化,因此要严格控制焙烤工艺.以带囊衣核桃仁作为研究材料,对不同温度和时间下焙烤的核桃仁进行了风味评定和油脂过氧化值的测定,得到125℃,4 h是油脂氧化程度最小而风味最佳的焙烤条件.     

成品发酵乳主要风味物质与风味指标的相关性研究

研究成品发酵乳在4℃、室温和37℃储存条件下主要风味物质的变化,包括羰基化合物乙醛、双乙酰以及挥发酸和酸性物质,同时考察发酵乳的风味强度和风味协调性等感官品评指标.结果显示发酵乳的主要风味化合物质量分数均呈增加趋势,且增长速度先快后慢.风味比较协调的发酵乳,其乙醛与双乙酰质量分数的比例在0.56-0.70之间.风味物质和风味评分分数的相关分析证明,发酵乳中的各风味化合物相关显著,且对发酵乳的风味强度和风味协调性均有不同程度的影响.     

Flavor and stability of pasteurized milk with elevated levels of conjugated linoleic acid and vaccenic acid

The objectives of this study were to determine if flavor differences between 2% fat pasteurized milks with and without naturally enhanced vaccenic acid (VA) and cis-9, trans-11 conjugated linoleic acids (CLA) levels could be detected over the commercial shelf life of the product and to determine if milk with elevated VA and cis-9, trans-11 CLA levels was more susceptible to development of light-induced oxidative flavor defects. Cows were fed a control diet or the same ration supplemented with 2% soybean oil and 1% fish oil (CLA diet). The milk, standardized to 2% fat, was pasteurized, homogenized, and stored in plastic containers at 4 degrees C. Oxidation was induced by exposing half of the containers to light. Testing was conducted at 1, 7, and 14 d postpasteurization. Average cis-9, trans-11 CLA content of the milks from the control and CLA diet groups was 0.52 and 4.74 g/100 g of fatty acids, respectively (8-fold increase). Average VA content of the milk from the control and CLA diet groups was 1.43 and 12.06 g/100 g of fatty acids, respectively (7.5-fold increase). Together, VA plus CLA represented almost 17% of the total milk fatty acids. There was no effect of light exposure on fatty acid composition initially or over the 14-d storage period. Although VA, cis-9, trans-11 CLA, and degree of unsaturation were significantly elevated in the milk from the CLA diet group, untrained panelists were unable to detect flavor differences initially or over time in 15 of 16 triangle test evaluations. Similarly, sensory results indicated no difference in susceptibility to the development of oxidized off-flavors between the milk from the control and CLA diet groups, even when oxidation was induced by light exposure.     

Effect of dietary antioxidant and increasing corn oil inclusion on milk fat yield and fatty acid composition in dairy cattle

The objective of this study was to examine the effect of a dietary synthetic antioxidant on feed intake, yields of milk and milk components and milk fatty acids (FA), in combination with increasing concentrations of dietary corn oil to provide increasing rumen unsaturated fatty acid load (RUFAL) challenges. Twenty-six Holstein cows (177 ± 57 d in milk; mean ± standard deviation) were assigned to treatment in a randomized complete block design. Treatments were a control diet (CON; n = 13 cows) or the same diet supplemented with a synthetic antioxidant (AOX; 6.1 g/d; dry blend of ethoxyquin and propyl gallate, Novus International Inc., St. Charles, MO; n = 13 cows). In period 1 (21 d), no supplemental corn oil was fed; in periods 2, 3, and 4 (14 d each), corn oil was supplemented at 0.7, 1.4, and 2.8% of the diet [dry matter (DM) basis] to incrementally increase RUFAL. For all variables measured, no significant interactions were detected between treatment and period, indicating no differences between the CON and AOX treatments at all levels of oil inclusion. Intake of DM was lower for AOX compared with CON but AOX had no effect on milk yield or milk fat concentration and yield. Milk protein yield and feed efficiency (energy-corrected milk/DM intake) tended to be greater for AOX compared with CON. Increasing dietary corn oil concentration (RUFAL) decreased DM intake, milk yield, milk fat concentration and yield, and feed efficiency. The AOX treatment increased the concentration and yield of 16-carbon milk FA, with no effect on de novo (<16 carbon) or preformed (>16 carbon) milk FA. Milk FA concentration of trans-10 C18:1, trans-10,cis-12 C18:2, and trans-9,cis-11 C18:2 were unaffected by AOX but increased with increasing RUFAL. In conclusion, supplementation with AOX did not overcome the dietary-induced milk fat depression caused by increased RUFAL.     

Vitamin A degradation and light-oxidized flavor defects in milk

To determine the effects of light exposure on vitamin A degradation and on light-oxidized flavor development, samples of whole, reduced fat, and nonfat milk were exposed to fluorescent light (either 1000 or 2000 lx) at time intervals of 2, 4, 8, or 16 h. Measurable vitamin A losses occurred at 2, 4, and 16 h at 2000 lx for nonfat, reduced fat and whole milk, respectively. Moderate light-oxidized flavors were detected after 4 h of light exposure (2000 lx) in the whole and reduced fat milk and after 8 h in nonfat milk. The different types of milk show a significant difference in relative flavor scores. By 16 h at 2000 lx, relative light-oxidized flavor development was lower in nonfat milk than in whole or reduced fat milk. The presence of milk fat appears to protect against vitamin A degradation in fluid products, but adversely affects the flavor quality of milk after exposure to light. In summary, these findings demonstrate that even a brief, moderate light exposure (2 h; 2000 lx) can reduce the nutritional value and flavor quality of fluid milk products.     

Differences in particle characteristics and oxidized flavor as affected by heat-related processes of milk powder

Understanding the formation of oxidized flavor will be highly useful in the improvement of milk powder quality. Effects of preheating, concentration and spray-drying on the particle characteristics and the oxidized flavor stability of milk powder were investigated. The surface composition and free radicals were analyzed using x-ray photoelectron spectroscopy and electron spin resonance spectrometry, respectively. The concentrations of selected oxidized volatiles hexanal and 2-heptanone were determined using solid-phase microextraction gas chromatography-mass spectrometry. Levels of hexanal and 2-heptanone in fresh milk powder were higher than those in raw milk and heated milk, which drastically increased with increasing time of storage. Differences in the morphological observations, free fat, and surface composition of fresh milk powder were found among different heat-related processes. During storage, a radical (g value, a characteristic constant whose value serves to identify any given free radical, was 2.0054) was detected in milk powder. The specific population of the radical increased from 2.99 × 10⁷ at 3 mo to 1.23 × 10⁸ at 6 mo of storage. Addition of ascorbic acid in milk powder changed the type of radicals and reduced the oxidation off-flavor. According to the Pearson correlations, not the surface compositions but the morphological characteristics of milk powder particles should be considered in maintaining the stability of oxidized flavor in storage.