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Wild mushrooms are used around the world in cooking. Now, Portuguese scientists have applied multivariate analysis to the gas chromatographs of volatiles from various species to build up a correlation pattern between the various compounds and the actual aroma. Such a correlation could be used by the food industry to verify product authenticity, allow flavour chemists to devise inexpensive additives that emulate the smell and taste of particular species, and biotechnologists to engineer new species with particular flavours. Paula Andrade, P. Guedes de Pinho, Bárbara Ribeiro, Rui Gonçalves, Patrícia Valentão, and Rosa Seabra of the University of Porto, and Paula Baptista of the Polytechnic Institute of Bragança, Saint Apolónia Campus, describe their observations in the Journal of Agricultural Food Chemistry. The researchers investigated the volatile and semivolatile components of eleven wild edible mushrooms, Suillus bellini, S. luteus, S. granulatus, Tricholomopsis rutilans, Hygrophorus agathosmus, Amanita rubescens, Russula cyanoxantha, Boletus edulis, Tricholoma equestre, Fistulina hepatica, and Cantharellus cibarius. These and many other species are found in the Trás-os-Montes region of northeastern Portugal, an area renowned as one of the richest regions in wild edible species. Andrade and colleagues used headspace solid-phase microextraction (HS-SPME) and liquid extraction combined with gas chromatography?mass spectrometry (GC−MS) to identify fifty volatile and non-volatile components formally. They also made a tentative identification of 13 other compounds. Based on "sensorial analysis" (smell), they researchers applied descriptors to these compounds as "mushroom like", "farm-feed", "floral", "honey like", "hay-herb", and "nutty". With all compounds classified by their odour the team then applied multivariate analysis (principal component analysis and agglomerative hierarchic cluster analysis) to the data. They were thus able to divide the edible mushrooms into three distinct groups. One group was rich in compounds containing eight carbon atoms, so-called C8 derivatives. These include the alcohols and ketones: 3-octanol, trans-2-octen-1-ol, 3-octanone, 1-octen-3-one, and 1-octen-3-ol. This latter compound is best described as smelling of "raw mushroom" and having a ?mushroom-like flavour?, and inevitably is considered to be the main component responsible for the most dominant flavour of all edible mushroom species. The second group is rich in terpene-type volatile compounds, hydrocarbons built from isoprene units. The third group contain high levels of methional, a sulfur-containing aldehyde with a strong musty and vegetable odour. Other compounds identified included esters, sterols, lactones, and terpenes, indole, and 3-chloroindole. While 1-octen-3-ol seems to give all species their mushroom-like flavour, the researchers point out that the myriad other organic compounds produced by the different species gives rise to their specific characteristics. "The presence and contents of these compounds give a considerable contribution to the sensory characteristics of the analyzed species," the researchers explain. Andrade and colleagues point out that the determination of volatile compounds and the building up of a characteristic profile for food stuffs using chemometrical comparisons of strains or species has become an essential part of the quality assessment process for checking authenticity of commercially available flavouring substances and food products. The distinctive odours of mushrooms species have also been used in taxonomy by mycologists hoping to identify and classify species. The researchers add that researchers in biotechnology have also screened several mushroom species in order to establish flavour profiles that might be engineered into novel species to give them particular flavour characteristics as well as allowing them to be cultivated commercially with ease. "As far as we know, this work is the first approach to the volatile characterization of these edible mushroom species," the researchers conclude. Their use of two extraction techniques coupled with GC-MS allowed them to identify a wide variety of compounds in each mushroom species investigated. The HS-SPME approach was best suited to extracting the volatile compounds, they add, whereas dichloromethane extraction was useful for the semivolatile compounds. Related links:
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