Adattamento e acclimatazione a diverse temperature di lieviti psicrofili obbligati e facoltativi e di lieviti mesofili. Studio della produzione di acidi grassi polinsaturi omega-3 e omega-6 per via fermentativa.

Adaptation and acclimation to different temperatures of obligate psychrophilic, facultative psychrophilic and mesophilic yeasts. Production of ω-3 and ω-6 polyunsaturated fatty acids by fermentative way. Obligate psychrophilic, facultative psychrophilic and mesophilic yeasts were cultured in a carbon rich medium at different temperatures to investigate if growth parameters, lipid accumulation and fatty acid composition were adaptive and/or acclimatory responses. Acclimation of facultative psychrophiles and mesophiles to lower temperature negatively affected their specific growth rate. Obligate psychrophiles exhibited the highest biomass yield (YX/S), followed by facultative psychrophiles, then by mesophiles. The growth temperature did not influence the YX/S of facultative psychrophiles and mesophiles. Acclimation to lower temperature caused the increase in lipid yield (YL/X) in mesophilic yeasts, but did not affect YL/X in facultative psychrophiles. Similar YL/X were found in both facultative and obligated psychrophiles, suggesting that lipid accumulation is not a distinctive character of adaptation to permanently cold environments. The extent of unsaturation of fatty acids was one major adaptive feature of the yeasts which colonize permanently cold ecosystems. Remarkable amounts of α-linolenic acid were found in obligate psychrophiles at the expenses of linoleic acid, whereas it was generally scarce or absent in all the others strains. Increased unsaturation of fatty acids was also an acclimatory response of mesophiles and facultative psychrophiles to lower temperature. It’s well known that omega-3 polyunsaturated fatty acids (PUFAs) display a variety of beneficial effects on various organ systems and diseases, therefore a process for the microbial production of omega-3 PUFAs would be of great interest. This work sought also to investigate if one of the better psychrophilic yeast, Rhodotorula glacialis DBVPG 4785, stimulated by acclamatory responses, produced omega-3 PUFAs. In fact, the adaptation of psychrophilic yeasts to cold niches is related to the production of higher amounts of lipids and to increased unsaturation degree of fatty acids, presumably to maintain membrane fluidity and functionality at low temperatures. Bioreactor fermentations of Rhodotorula glacialis DBVPG 4785 were carried out at 25, 20, 15, 10, 5, 0, and -3°C in a complex medium with high C:N ratio for 15 days. High biomass production was attained at all the temperatures with a similar biomass/glucose yield (YXS), between 0.40 and 0.45, but the specific growth rate of the strain decreased as the temperature diminished. The coefficients YL/X have been measured between a minimum of 0.50 to a maximum of 0.67, but it was not possible to show a clear effect of temperature. Similarly, the coefficient YL/S ranges from a minimum of 0.22 to a maximum of 0.28: again, it does not appear to be any significant changes due to temperature. Among omega-3 PUFAs, only α-linolenic acid (ALA, 18:3n-3) was found at temperatures below to 0°C, while, it’s remarkable, that the worthy arachidonic acid (C20:4,n-6), stearidonic acid (C20:4,n-3) C22:0 and docosahexaenoic acid (C22:6n-3) were produced only at the late exponential phase and the stationary phase of batch fermentations at 0 and -3°C. The docosahexaenoic acid (DHA) is a beneficial omega-3 PUFA that is usually found in fatty fish and fish oils. The results herein reported improve the knowledge about the responses which enable psychrophilic yeasts to cope with cold and may support exploitation of these strains as a new resource for biotechnological applications.

Application of different instrumental techniques to the selective evaluation of bio-sensible compounds in foodstuff of animal and vegetable origin

This PhD thesis describes the application of some instrumental analytical techniques suitable to the study of fundamental food products for the human diet, such as: extra virgin olive oil and dairy products. These products, widely spread in the market and with high nutritional values, are increasingly recognized healthy properties although their lipid fraction might contain some unfavorable components to the human health. The research activity has been structured in the following investigations: “Comparison of different techniques for trans fatty acids analysis” “Fatty acids analysis of outcrop milk cream samples, with particular emphasis on the content of Conjugated Linoleic Acid (CLA) and trans Fatty Acids (TFA), by using 100m high-polarity capillary column” “Evaluation of the oxidited fatty acids (OFA) content during the Parmigiano-Reggiano cheese seasoning” “Direct analysis of 4-desmethyl sterols and two dihydroxy triterpenes in saponified vegetal oils (olive oil and others) using liquid chromatography-mass spectrometry” “Quantitation of long chain poly-unsatured fatty acids (LC-PUFA) in base infant formulas by Gas Chromatography, and evaluation of the blending phases accuracy during their preparation” “Fatty acids composition of Parmigiano Reggiano cheese samples, with emphasis on trans isomers (TFA)”

Functional components and lipid quality assessment in vegetable foods: analytical and technological approaches

Lipids are important components that contribute very significantly to nutritional and technological quality of foods because they are the least stable macro-components in foods, due to high susceptibility to oxidation. When rancidity take place, it makes food unhealthy and unacceptable for consumers. Thus, the presence of antioxidants, naturally present of added to foods, is required to enhance shelf life of foods. Moreover, antioxidant like phenolic compounds play an important role in human health enhancing the functionality of foods. The aim of this PhD project was the study of lipid quality and lipid oxidation in different vegetable foods focusing on analytical and technological aspects in order to figure out the effects of lipid composition and bioactive compounds (phenolic compounds, omega-3 fatty acids and dietary fiber) addition on their shelf life. In addition, bioavailability and antioxidant effects of phenolic compounds in human and animals, respectively, were evaluated after consumption of vegetable foods. The first section of the work was focused on the evaluation of lipid quality impact on technological behaviour of vegetable foods. Because of that, cocoa butter with different melting point were evaluated by chromatographic techniques (GC, TLC) and the sample with the higher melting point showed the presence of fatty acids, triglycerides, 2-monoglycerides and FT-IR profile different from genuine cocoa butter, meaning an adding of foreign fat (lauric-fat) not allowed by the law. Looking at lipid quality of other vegetable foods, an accelerated shelf life test (OXITEST®), was used to evaluate of lipid stability to oxidation in tarallini snacks made up using different lipid matrices (sunflower oil, extravirgin olive oil and a blend of extravirgin olive oil and lard). The results showed a good ability of OXITEST® to discriminate between lipid unsaturation and different cooking times, without any samples fat extraction. In the second section, the role of bioactive compounds on cereal based food shelf life was studied in different bakeries by GC, spectrophotometric methods and capillary electrophoresis. It was examined the relationships between phenolic compounds, added with flour, and lipid oxidation of tarallini and frollini. Both products showed an increase in lipid oxidation during storage and antioxidant effects on lipid oxidation were not as expected. Furthermore, the influence of enrichment in polyunsaturated fatty acids on lipid oxidation of pasta was evaluated. The results proved that LC n-3 PUFA were not significantly implicated in the onset of oxidation in spaghetti stored under daylight and accelerated oxidation in a laboratory heater. The importance of phenolic compounds as antioxidant in humans and rats was also studied, by HPLC/MS in the latter section. For this purpose, apigenin and apigenin glycosides excretion was investigated in six women’s urine in a 24 hours study. After a single dose of steamed artichokes, both aglicone and glucuronide metabolites were recovered in 24 h urine. Moreover, the effect of whole grain durum wheat bread and whole grain Kamut® khorasan bread in rats were evaluated. Both cereals were good sources of antioxidants but Kamut® bread fed animals had a better response to stress than wheat durum fed, especially when a sourdough bread was supplied.