Monitoring of virgin olive oil volatile compounds evolution during olive malaxation by an array of metal oxide sensors

In addition to the sanitary aspects of production and the genetic and/or geographic origin of the drupes olive malaxation is a critical control point of virgin olive oil (VOO) production from a qualitative point of view. In particular the sensory peculiarities of malaxation are determined by the presence of C₆ and C₅ aldehydes and alcohols in the VOO head space due to lipoxygenase activity. On-line monitoring of the evolution of these substances during VOO processing could be very useful for defining the operative conditions of malaxation (i.e. time and temperature) in order to improve the VOO sensory quality according to product type.     

Coupling MOS sensors and gas chromatography to interpret the sensor responses to complex food aroma: Application to virgin olive oil

This paper describes a novel approach to determine the individual contribution of volatile compounds to the overall sensor responses of metal oxide semiconductor (MOS) sensors when they are applied to a complex mixture of compounds such as food aroma. A methodology entailing the use of a sensor array or electronic nose (EN) as non-destructive detector in-parallel with the flame ionization detector of a gas chromatograph (GC) is described and illustrated in the context of virgin olive oil aroma analysis. Aspects related to the experimental set up and data processing are examined. The capability of gas chromatography for obtaining qualitative and quantitative information of the volatile compounds present in virgin olive oil was used to find relationships between these compounds and the sensor responses by means of a coupled system GC–EN. The sensor responses that resulted from this coupling (sensorgrams) served to prove the sensor sensitivity to alcohols, aldehydes, and those compounds that are responsible to sensory defects in virgin olive oil (e.g. aldehydes and acids).     

Effect of initial headspace oxygen level on growth and volatile metabolite production by the specific spoilage microorganisms of fresh-cut pineapple

The effect of initial headspace (IH) O₂ level on the shelf-life of fresh-cut pineapple was evaluated in this study. The results showed that although the IH O₂ level had a minor effect on the growth of Candida argentea, Candida sake and Meyerozyma caribbica on pineapple agar, the quantities of the volatile organic metabolites produced by these yeasts was generally smaller the lower the IH O₂ level. The only exception was the production of ethyl acetate by C. argentea, which was higher at low IH O₂ levels. In triangle tests performed with trained panellists, pineapple cubes packaged in an IH of 5% O₂ were determined to be significantly different (P < 0.05) to those packaged in 21% O₂ from day 5 of storage. Preference was shown for the pineapple cubes packaged in an IH of 5% O₂. The results imply that packaging in an IH O₂ level of 5% could be used to extend the shelf-life of fresh-cut pineapple.     

Classification of Pecorino cheeses using electronic nose combined with artificial neural network and comparison with GC–MS analysis of volatile compounds

An electronic nose based on an array of 6 metal oxide semiconductor sensors was used, jointly with artificial neural network (ANN) method, to classify Pecorino cheeses according to their ripening time and manufacturing techniques. For this purpose different pre-treatments of electronic nose signals have been tested. In particular, four different features extraction algorithms were compared with a principal component analysis (PCA) using to reduce the dimensionality of data set (data consisted of 900 data points per sensor). All the ANN models (with different pre-treatment data) have different capability to predict the Pecorino cheeses categories. In particular, PCA show better results (classification performance: 100%; RMSE: 0.024) in comparison with other pre-treatment systems.     

The volatile fraction profiling of fresh tomatoes and triple concentrate tomato pastes as parameter for the determination of geographical origin

Two unsupervised pattern recognition techniques such as stepwise linear discriminant analysis (SLDA) and Soft Independent Modeling of Class Analogy (SIMCA) were used to classify tomato samples in categories corresponding to the cultivation areas. The same approach was used for triple concentrated pastes for discrimination between two different Italian production areas. Accordingly, HS-SPME-GC-MS with 85 ??m carboxen/polydimethylsiloxane fiber was used for the determination of the volatile fraction in tomatoes and triple concentrate tomato pastes samples. Ethyl isobututanoate was used as internal standard for semiquantitative analysis and the concentration data (??g/kg) of 38 compounds for tomatoes and of 32 compounds for triple concentrates were used in following chemometric analysis. Sixteen and three variables were selected by forward stepwise LDA for tomatoes and pastes, respectively. SLDA and SIMCA models showed respectively 96% and 94% in term of prediction ability for tomatoes. The two supervised techniques provided 100% and 97% in prediction of the production areas of tomato pastes, respectively.     

A simple wheat germ diet for studying the nutrient requirements of the Indian meal moth, Plodia interpunctella (Hübner)

Indian meal moth infestation of processed cereal products during storage could be managed with little or no use of conventional pesticides if there was a greater recognition and use of the moth's innate vulnerabilities. Slowing the growth rate of the infesting larvae is a simple strategy that can decrease the amount of damage and decrease the frequency of pesticide intervention. The growth rates of Indian meal moths on different cereal products varies widely indicating product-related differences in nutrient availability for the insects. Nutrient availability depends upon both the amounts of nutrients available in the cereal product and upon physical characteristics of the product that restrict the assimilation of nutrients.

The development of control strategies for protecting processed cereal products based upon nutrient availability requires a simple, palatable test diet of known composition. Wheat germ mixed with 30% glycerol (w/w) provides a suitable growth medium for the Indian meal moth whose nutrients have been largely identified and quantified. Our studies indicate that dietary glycerol augments Indian meal moth growth and development on wheat germ by moisturizing the diet and probably provides a source of carbon and energy for larval growth.     

Quality changes during storage of cooked and sliced meat products measured with PTR-MS and HS-GC–MS

The changes in the VOC composition of industrially produced saveloy were measured with Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS) and HeadSpace Gas chromatography–mass spectrometry (HS-GC–MS) during a six weeks storage period. A decrease in the volatile organic compounds contributing to the fresh aroma of saveloy was the main change observed with both PTR-MS and HS-GC–MS. Samples of four other types of cooked and sliced meat product were measured with PTR-MS in the middle and at the end of the four week shelf-life period. These measurements showed an increase in m/z 69, 71, 87 and 89 for the pork loin and in m/z 61 for the herbal saveloy samples. These ions were assigned to the microbial spoilage markers: acetic acid, 2- and 3-methylbutanol, 2- and 3-methylbutanal, diacetyl and acetoin. Overall, this study shows that PTR-MS has potential for quality control of cooked and sliced meat products.     

Volatile components in flavour concentrates from crayfish processing waste

Volatile components in flavour concentrates prepared from crayfish (Procambarus clarkii Girard) processing waste at two temperatures (85°C and 100°C) were compared. The presence of 121 compounds was established. Among these, 78 compounds were positively identified of which 50 were detected in crayfish for the first time. These compounds were mainly N- and S-containing compounds, ketones and aldehydes. The amounts of aldehydes and ketones were 1.5 and 1.4 times higher in the 85°C concentrates, respectively; and the amounts of N-containing compounds were 2.3 times higher in the 100°C concentrates.     

Diversity and technological potential of lactic acid bacteria of wheat flours

Lactic acid bacteria (LAB) were analysed from wheat flours used in traditional bread making throughout Sicily (southern Italy). Plate counts, carried out in three different media commonly used to detect food and sourdough LAB, revealed a maximal LAB concentration of approximately 4.75 Log CFU g⁻¹. Colonies representing various morphological appearances were isolated and differentiated based on phenotypic characteristics and genetic analysis by randomly amplified polymorphic DNA (RAPD)-PCR. Fifty unique strains were identified. Analysis by 16S rRNA gene sequencing grouped the strains into 11 LAB species, which belonged to six genera: Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Weissella. Weissella cibaria, Lactobacillus plantarum, Leuconostoc pseudomesenteroides and Leuconostoc citreum were the most prevalent species. The strains were not geographically related. Denaturing gradient gel electrophoresis (DGGE) analysis of total DNA of flour was used to provide a more complete understanding of the LAB population; it confirmed the presence of species identified with the culture-dependent approach, but did not reveal the presence of any additional LAB species. Finally, the technological characteristics (acidifying capacity, antimicrobial production, proteolytic activity, organic acid, and volatile organic compound generation) of the 50 LAB strains were investigated. Eleven strains were selected for future in situ applications.     

电子鼻技术在果蔬病害检测中的研究进展

归纳和总结了近年来电子鼻技术在果蔬采后单种和多种病原菌侵染检测中的最新研究成果,分析了当前电子鼻技术存在的缺点,预测了电子鼻技术在果蔬病害检测中的发展方向。     

动态顶空进祥分析啤酒的挥发性风味化合物

研究了采用动态顶空进样技术分析啤酒的挥发性风味化合物的方法。以高纯氮吹出并吸附于Tenax GC上的挥发性组份经加热脱附后直接注入毛细管色谱柱,将这一装置与GC-MS相连,从啤酒中检出了19种化合物,对其中的13种作了定量测定,方法具有良好的重现性和回收率。     

啤酒酵母自溶条件的优化及其抽提物的挥发性风味成份

本文研究了添加硫胺素、葡萄糖、缓慢加热对啤酒酵母自溶的影响,正交试验表明:pH5.5、温度57℃、添加硫胺素0.10％(W/W)、升温时间60分可使自溶时间缩短至6～8小时。 本文还研究了添加中性蛋白酶1398的酵母自溶。在正交试验选出的条件下,自溶时间及蛋白质、氨基酸得率都不及前述工艺。 用SDE分离得到自溶抽提物的挥发物,并用GC-MS鉴定了63化合物。其中含硫化合物20个。