Short communication: Chemical-sensory and volatile compound characterization of ricotta forte,a traditional fermented whey cheese

Ricotta forte is a traditional whey cheese, obtained through natural fermentation of fresh ricotta, that is getting increasing attention by food traders. In view of possible initiatives for its valorization, the chemical and sensory characteristics were investigated. Samples were obtained from 14 different manufacturer, and were subjected to chemical, biochemical, volatile organic compound, and sensory analyses. All samples presented low pH with high moisture (62–66%) and fat content (57–60% on dry matter). From a biochemical point of view, the electrophoretic patterns evidenced that β-lactoglobulin was the main protein present at all sample ages. Only intermediate levels of proteolysis (20.69% ripening index) took place during aging, whereas the main biochemical event in this dairy product was lipolysis (2.10 mEq/g of acid degree value). Accordingly, free fatty acids dominated the volatile organic compound profile and strongly influenced the sensory characteristics with flavor described as rancid, pungent, acrid, and smelly feet: all associated with short-chain fatty acids such as acetic, propionic, butyric, and caproic. Finally, the sample age did not influence chemical composition, whereas it had significant effect on lipolysis and flavor intensity.     

Characterization of volatile compounds in fermented milk using solid-phase microextraction methods coupled with gas chromatography-mass spectrometry

Lactic acid bacteria (LAB) are industrially important bacteria that are widely used in the fermented food industry, especially in the manufacture of yogurt. Characteristic flavors are produced by LAB during fermentation and storage that affect the quality and acceptability of fermented milk products. In this study, the volatile compounds in milk fermented by Streptococcus thermophilus IMAU80842 alone, Lactobacillus delbrueckii ssp. bulgaricus IMAU20401 alone, or both species together were identified using solid-phase microextraction methods coupled with gas chromatography-mass spectrometry. A total of 53, 43, and 32 volatile compounds were identified in milk fermented by S. thermophilus alone, L. delbrueckii ssp. bulgaricus alone, or both species together, respectively. The presence of some important flavor compounds was confirmed: acetic acid, acetaldehyde, acetoin, 2,3-butanedione, ethanol, and 1-heptanol. Our results demonstrate that the composition of the volatile compounds in fermented milk depends on the species of LAB used and whether they are used alone or in combination. This is important for the selection of appropriate starter cultures for the production of different types of fermented milk product with particular flavors.     

Comparison of microbiota and volatile organic compounds in milk from different sheep breeds

In this study, we compared the microbiota and volatile organic compounds (VOC) present in the milk obtained from 3 different sheep breeds, namely Merino, Lacaune, and Assaf. Udder milk was collected from 21 animals, 7 from each breed. Bacterial microflora was determined metagenomically by extracting the DNA from the milk and analyzing the V3-V4 region of the 16S rRNA gene. Headspace solid-phase microextraction gas chromatography-mass spectrometry method was used to analyze VOC. The metagenomic analysis revealed (for Merino, Lacaune, and Assaf milk, respectively) Firmicutes (66.32, 69.36, and 57.08%), Actinobacteria (19.09, 7.67, and 19.40%), Proteobacteria (13.76, 21.06, and 22.19%), and Bacteroidetes (0.84, 1.91, and 1.33%) phyla in the milk samples. Lactobacillus was highly abundant in the milk of 3 breeds (29.64, 43.50, and 18.70%). The genera constituting more than 2% of all bacteria in all groups were Jeotgalicoccus (7.19, 5.34, and 10.77%), Enterococcus (5.18, 9.78, and 3.64%), and Corynebacterium (4.08, 3.00, and 13.44%). A total of 32 different VOC were identified by headspace solid-phase microextration analysis with 9, 30, and 24 different compounds from Merino, Lacaune, and Assaf breeds, respectively. Although ketone was the most abundant compound in Merino milk (71.84%), hydrocarbons were the most detected in Lacaune and Assaf milk (37.18% and 55.42%, respectively). A positive correlation was found between acetone, which was detected at the highest level in all groups, with Salinicoccus, Alloiococcus, Psychrobacter, and Dietzia. In addition, a negative correlation was found between the Lactobacillus genus, detected at the highest level in all groups, with methyl cyclopentane, 3-methylheptane, octane, decane, 3,3-dimethyloctane, and dodecane. Thus, differences were observed in the bacterial microflora and VOC in the sheep milk from different breeds under different feeding and breeding conditions.     

Volatile compounds of Chinese Luzhou flavoured liquor distilled from grains fermented in 100 to 300 year-old cellars

Baijiu – Chinese white spirits – contain a plethora of volatile compounds of which only some have been identified. This study reports two pre-treatments, direct injection and headspace solid phase microextraction (HS-SPME), coupled with gas chromatography mass spectrometry to analyse the volatile compounds of liquor distilled from grains fermented in 100-, 200- and 300 year-old cellars. Three samples from each cellar were analysed and 71 compounds were detected using direct injection with 75 compounds detected using HS-SPME. The compounds included esters, alcohols, carboxylic acids, aldehydes and ketones and other compounds. Although both methods detected a similar number of compounds, the types of compounds detected differed. The collection times of the samples were divided into four stages according to their composition. This study provides an analytical foundation for further determining components in baijiu. © 2019 The Institute of Brewing & Distilling     

Volatile organic compounds profile during milk fermentation by Lactobacillus pentosus and correlations between volatiles flavor and carbohydrate metabolism

Flavor, as one of the most important properties determining the acceptability and preference of fermented milks, is influenced by compositional and processing factors. In this study, we focused on the volatile organic compounds related to flavor during milk fermentation by Lactobacillus pentosus according to electronic nose analysis. Xylose (1% addition) metabolized by Lb. pentosus strongly affects the flavor of yogurt, with the potent volatile organic compounds of ethanol (3.08%), 2,3-butanedione (7.77%), and acetic acid (22.70%) detected using solid-phase microextraction coupled with gas chromatography-mass spectrometry analysis. Sensoryanalysis also showed skimmed yogurt fermented by Lb. pentosus with 1% xylose had the unique scores of sourness (acetic acid) and butter flavor (2,3-butanedione). Furthermore, α-acetolactate synthase and α-acetolactate decarboxylase in carbohydrate metabolism play important roles in milk fermentation. Under preferable conditions (pH 5.5, 42°C) for α-acetolactate synthase and α-acetolactate decarboxylase, the relative content of potent flavor compound 2,3-butanedione was 10.13%, which was 2.55% higher than common culture condition (pH 4.5, 37°C), revealing that xylose metabolized by Lb. pentosus has potential values for the milk product industry, such as the acceptability and preference of fermented milk product.     

Optimization of equilibrium headspace analysis of volatile flavor compounds of malaysian soursop (Annona muricata): Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS)

Headspace solid-phase microextraction (HS-SPME) coupled to comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) was applied for equilibrium headspace analysis of Malaysian soursop (Annona muricata) volatile flavor compounds. A two-level fractional factorial design (2^5-1) was used to determine the effect of SPME variables, namely, SPME fibers, adsorption temperature, extraction time, amount of salt, sample amount and sample concentration on the extraction efficiency of volatile flavor compounds. A total of 37 volatile compounds were identified, comprising 21 esters, 6 alcohols, 3 terpenes, 2 acids, 2 ketones, 2 aldehydes and an aromatic with different hydrophobicities (log P) ranging between −0.14 and 4.83. Extraction using 10 g of diluted (5% w/w) blended soursop pulp with CAR/PDMS fiber at 25 °C for 30 min and 30% (w/w) of NaCl under stirring mode resulted in the highest extraction efficiency of volatile flavor compounds. The principal component analysis score discriminated the influence of SPME variables on the equilibrium headspace concentration of target volatile compounds.     

不同类型腊肉挥发性风味成分的比较研究

利用电子鼻和固相微萃取气相色谱-质谱联用技术研究湖南腊肉、四川腊肉和广式腊肉三种类型腊肉挥发性风味成分的差异性。对电子鼻传感器信号数据进行主成分分析发现,广式腊肉与其他两种类型香气特征差异显著,湖南腊肉和四川腊肉二者香气特征较为相似。腊肉中分别检测出了32种、38种和42种挥发性风味成分,包括碳氢类、醇类、醛类、酮类、酯类和呋喃类化合物。三类腊肉被鉴定出的共有成分仅包括十一烷、十二烷、十四烷和植烷4种挥发性成分。四川腊肉和湖南腊肉被鉴定出的共有成分包括2-甲基苯酚、愈创木酚、4-乙基愈创木酚、5-甲基愈创木酚、糠醇等25种挥发性成分。而在广式腊肉中鉴定出了大部分的醇类、醛类和全部的酯类化合物,而没有鉴定出酚类和呋喃类化合物。本研究为传统腊肉加工的中特征性风味的形成与调控提供理论依据。     

Differentiation of fresh and frozen/thawed fish, European sea bass (Dicentrarchus labrax), gilthead seabream (Sparus aurata), cod (Gadus morhua) and salmon (Salmo salar), using volatile compounds by SPME/GC/MS

BACKGROUND: A simple method based on solid phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS) was applied for studying the volatile profiles of whole fish samples of European sea bass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) and fillets of cod (Gadus morhua) and salmon (Salmo salar) during frozen storage in order to be able to differentiate a fresh product from one that has been frozen. Analysis of volatile compounds was performed on these two product types, fresh and after freezing/thawing following storage at ? 20 °C for 30 and 90 days. RESULTS: More than a hundred volatile compounds were found by SPME/GC/MS. Statistical processing by principal component analysis and ascending hierarchical classification was used to classify the samples into categories and verify the possibility of separating fresh samples from those that had been frozen and thawed. The compounds to be used as differentiators were identified. Four compounds were common to all species: dimethyl sulfide, 3‐methylbutanal, ethyl acetate and 2‐methylbutanal. Not only were they found in larger quantities after thawing but they also increased with the duration of storage at ? 20 °C. CONCLUSION: These four compounds can therefore be considered as potential markers of differentiation between a fresh product and one that has been frozen. Copyright © 2012 Society of Chemical Industry     

微波辅助萃取-固相微萃取-气相色谱-质谱法分析花椒香气成分

采用微波辅助萃取与顶空-固相微萃取联合(MAE-HS-SPME)的方法萃取花椒香气成分,用气相色谱-质谱(GC-MS)法分析,并将分析结果与同时蒸馏萃取(SDE)和HS-SPME法对比.结果表明,MAE-HS-SPME的最佳条件为:称取10 g样品,加入100 mL去离子水,微波功率为120 W,用100μm PA萃取头萃取5 min,250℃解吸20 s.GC-MS分析确认了59种成分,占总峰面积的96.65%;三种方法所得主要成分相同,均为芳樟醇、乙酸芳樟酯等;MAE-HS-SPME法鉴定出的成分较多,说明MAE-HS-SPME是一种高效的样品前处理方法.     

Enantiomeric fraction of selected chiral polychlorinated biphenyls in cow, goat, and ewe milk and dairy products by heart-cut multidimensional gas chromatography: first results

The concentration of the most relevant polychlorinated biphenyl (PCB) congeners has been determined in milk and dairy products (i.e., cheese and yogurt, from cow, goat, and ewe). In addition, the enantiomeric composition of 11 atropisomeric PCB has been determined for the first time in this type of product, using heart-cut multidimensional gas chromatography and 2 enantioselective columns for the unambiguous determination of both enantiomers. Results showed a deviation from the racemic composition for PCB 135, 136, 176, 171, and 183 in the samples analyzed. Whereas PCB 135, 136, and 176 showed an enrichment of the first eluted enantiomer, congeners 171 and 183 showed an enrichment of the first or second eluted enantiomer depending on the dairy product and species. The remaining congeners analyzed (PCB 84, 91, 95, 132, 149, and 174) did not present a clear enrichment of any of the enantiomers. Therefore, differences in the enantiomeric composition of some of the target atropisomeric PCB have been found among the 3 species and among the milk samples and the related dairy products analyzed. Enantioselective species-dependent processes, as well as enantioselective processes carried on by microorganisms during the fermentation and ripening in the latter could be possible explanations for the differences observed. However, changes in the enantiomeric composition are still not well understood, and further investigation in this direction is recommended.     

Determination of volatile compounds to characterize fish spoilage using headspace/mass spectrometry and solid‐phase microextraction/gas chromatography/mass spectrometry

Changes in volatile compounds were monitored in whiting (Merlangius merlangus), cod (Gadus morhua) and mackerel (Scomber scombrus) and related to spoilage. Data are presented from headspace/mass spectrometric (HS/MS) analysis and solid‐phase microextraction/gas chromatographic/mass spectrometric (SPME/GC/MS) analysis at two time points (day 0 and day 10) during storage at 4 °C. HS/MS revealed 24 ions that could be used as markers of spoilage. SPME/GC/MS identified 86 compounds, 20 of which could perhaps be used to characterize freshness: principally alcohols, ketones, aldehydes and C₂–C₁₁ esters. Compounds common to the three species studied appear to be generated by microbial degradation. Copyright © 2005 Society of Chemical Industry     

渥堆黑茶香气和主要功效研究进展

为探究不同种类黑茶香气成分特征,采用顶空固相微萃取和气相色谱-质谱联用技术（Headspace solid-phase microextraction-gas chromatography-mass spectrometry,HS-SPME-GC-MS）结合感官审评对茯砖茶、黑砖、藏茶、六堡茶、天尖等五种主要黑茶样品的香气成分进行分析。结果表明,五种黑茶的香气特征明显。茯砖茶主要香气轮廓为菌花香和陈香,六堡茶具有明显持久的槟榔香与陈香,藏茶具有持久的陈香,黑砖茶香气纯正,天尖具有持久的松烟香。五种黑茶样品的感官审评总分排序为藏茶（91.35）>茯砖茶（90.15）>黑砖（89.05）>六堡茶（88.85）>天尖（86.33）;五种不同的黑茶共含有56个香气成分,不同种类黑茶在香气成分构成与含量上均有差异。五种黑茶样品的香气成分总含量排序为茯砖茶（6355.30 μg/L）>藏茶（5858.73 μg/L）>黑砖（5789.71 μg/L）>天尖（4801.37 μg/L）>六堡茶（3740.14 μg/L）。根据多元统计分析以及香气活性值分析,发现1,2,3-三甲氧基苯对藏茶的陈香具有突出贡献。反,反-2,4-癸二烯醛、反,反-2,4-壬二烯醛、柠檬醛I、柠檬醛II、正己醛和水杨酸甲酯对茯砖茶的菌花香具有突出贡献,而1,2,3-三甲氧基苯则对茯砖茶的陈香具有突出贡献。（+）-雪松醇对六堡茶的槟榔香具有突出贡献。反,反-2,4-癸二烯醛、反,反-2,4-壬二烯醛、正己醛和植醇等对天尖的松烟香有突出贡献。苯乙醇、橙花叔醇II和氧化芳樟醇I等香气成分的综合作用形成了黑砖纯正的香气。本研究为探索不同种类黑茶的香气品质提供了数据参考。     

Effects of technological settings on yield,curd, whey,and cheese composition during the cheese-making process from raw sheep milk in small rural dairies: Emphasis on cutting and cooking conditions

The technological conditions of cheese-making affect cheese yield and compound losses in the whey, especially the processes of cutting and cooking. Although significant compositional and functional differences have been reported among animal species, there is a lack of studies on the effects of cheese-making technology on cheese yield and losses for sheep milk. Thus, we examined the cheese-making settings in 8 small rural dairies working with raw sheep milk and their effects on cheese yield and compound losses in whey during the cheese-production season. Actual cheese yield varied in 2 to 3 kg of cheese/100 kg of milk among dairies due to the cheese-making conditions, particularly the duration of cutting and cooking and the final cooking temperature. The combination of the conditions used during cutting and cooking, especially, determined fat losses in the whey. Fat losses were increased with high-speed and short cutting time settings together with high stirring speed and long duration of cooking. Additionally, cheese-makers should adapt the cutting and cooking conditions to the seasonal variations of milk composition, especially during early summer, when fat losses in the whey are higher. Our results suggest that it could be useful to use approximately 10 to 15 min of cutting time and moderate cooking speed and duration. The data reported in this study may assist the improvement of the cheese-making process in small rural dairies using sheep milk, where facilities are limited and the role of the cheese-maker is crucial.