Effect of thermal and nonthermal processes on selected physicochemical parameters of vegetables

The increasing request of fruit and vegetables is bringing the food industry, together with the academia, to improve the processes targeted to prolong the crops shelf-life. Preservation of foods usually involves technologies that prevent microbial growth and retard enzymatic quality degradation reactions. Traditionally, thermal processing (≥90 °C) and freezing (≤−40 °C) have formed the core of food preservation. During freezing, the ice crystal formation causes damages of vegetables cells walls. Furthermore, frozen vegetables are previously blanched and consumed cooked, so they are subjected also to the detrimental effect of thermal treatment. Novel nonthermal technologies are one of the alternatives currently available for the preservation of vegetables because they accomplish inactivation of microorganisms and enzymes but minimize adverse thermal exposure. Among them, the use of high hydrostatic pressures for food processing is finding increased application within the food industry. Despite several studies have been conducted on the effect of processes on vegetables, a lack of literature is still present, because of the fragmented investigation of the effect of traditional methods and still poor data on the novel technologies. Based on these considerations, the present PhD thesis deals with the evaluation of the effect of different conventional and innovative preserving technologies on vegetables by means of selected physico-chemical properties. Different approaches were investigated to reach this goal. In the first part of this PhD thesis, the evaluation of the effect of different steps of a conventional industrial freezing process was investigated on asparagus, zucchini and green beans. Samples were examined in all the stages of production “from farm to fork” as raw/uncooked (control test), blanched, boiled from the raw samples and after industrial freezing. A deep investigation was carried out to evaluate qualitative (texture and colour), histological and nutritional (antioxidant activity and bioactive compounds) aspects. The obtained results will show how manufacturers and researchers have to join together in order to develop industrial freezing process conditions according to the matrix of vegetable, with the final aim being to offer the end-user consumer high quality frozen products. In the second part of the thesis, the evaluation of different cooking methods as preservation technique for vegetables was investigated. There is a general lack of study in literature on the effect of cooking on the main quality attributes (i.e. texture, colour) that have a great impact on the final consumer acceptance of vegetables. When taken into consideration, only a single type of heating treatment or one quality attribute was discussed. Thus, this topic needs to be more deeply investigated with the ultimate goal to offer a higher quality final cooked product to the consumers, achieving a greater retention of the original quality of the processed vegetable. Starting from this observation, in a first study the effect of three common cooking procedures (boiling, steaming and microwaving) on structure, texture and colour of carrots processed in an industrial plant was studied and the obtained results were compared with those obtained from raw carrots provided by the same manufacturer and cooked with the same procedures. Then, a relatively new little explored cooking approach, the combined air/steam cooking, was the object of another investigation. Several air/steam cooking time/temperature conditions were selected and applied on two commonly used vegetables, as pumpkin and Brussels sprouts, selected on the basis of their different nutritional values and physical characteristics. The results obtained in term of cooking (cooking values, weight loss), physical (texture and colour) and nutritional (antioxidant activity and phenol contents) parameters were compared with those obtained cooking the same vegetables with a common steaming procedure. In the third part of the thesis, the impact of a novel non thermal technology, such as high hydrostatic pressure process was studied at the Centre for nonthermal treatment of food”of the Washington State University of Pullman (WA) on beetroot, which presents a well-known high nutritional value. In particular, the effect of pressure treatment realized at 650 MPa and a temperature of 21°C was studied taking into account different times of processing evaluating physico-chemical, enzymatic and nutritional aspects. The obtained results were compared to the raw product and those treated with classical thermal treatments as blanching and canning. The preliminary findings obtained in this part of the thesis work, suggested that the high hydrostatic pressure treatment could be used as valid alternative for the preservation of beetroots, being less invasive than canning and quite comparable with blanching. In the last part of this PhD work, a novel spectroscopical approach as Raman spectroscopy was used for the evaluation of carotenoid pattern changes after different cooking treatments on carrots. Changes on carotenoid profiles measured by means of Raman spectroscopy were compared with their quantitative determinations acquired by the high-performance liquid chromatography and the colour parameters finding good statistical correlations among techniques. In conclusion, this PhD thesis revealed the strengths and weaknesses of both the traditional thermal and novel nonthermal vegetable treatments. In general, while the freezing and cooking traditional methods resulted in an extended modification of the quality parameters, the high pressure treated samples revealed a better preservation degree. The extent of the modifications observed after the application of both thermal or nonthermal processes was however related to the type of vegetable and the process conditions, therefore this finding should encourage to research and plan specific processing conditions. A big effort was given to the use of novel analytical technology, such as Raman spectroscopy, for the fast and easy way to obtain real time information on the chemical transformation of the nutrients under treatment

Chemical composition and thermal behaviour of tropical fat fractions from solvent-assisted process: a review

Fractional crystallization is a process applied to plant and animal fats to obtain fat products with new functional properties and nutritional values. Fractionation is generally performed through either a dry or a solvent-assisted process. As solvents can wash off the liquid molecules able to entrap the solid component inside, the solvent-crystallization seems to be more efficient than other fractionation procedures. In recent times, fractional crystallization has been investigated for avocado (Persea Americana) butter, engkabang (Shorea macrophylla) fat, palm oil-moringa oil blend, and mee fat (Madhuca longifolia) to prepare solid (stearin) and liquid (olein) fractions. This review sums up the main and recent published studies on chemical and thermal (upon differential scanning calorimetry) properties of fat fractions obtained using solvent-assisted process. It has been argued that the ease of a fat fractionation mainly depends on the thermal characteristics of its triacylglycerol molecules. Fats with low-and high-melting thermal transitions in wide separation would yield fat components with remarkable changes in physico-chemical characteristics, fatty acid and triacylglycerol compositions as well as thermal profiles. The activities involving the use of fat components, during food formulation, may significantly benefit from a further learning of the fats behavior

Effects of high hydrostatic pressure on physico-chemical and structural properties of two pumpkin species

The effects of high pressure treatments (200, 400, 600MPa for 5 min) and a thermal treatment (85°C for 5 min) were evaluated on cubes of two pumpkin species (Cucurbita maxima L. var. Delica and Cucurbita moschata Duchesne var. Butternut) up to 2 months of refrigerated storage. Increasing the pressure, small parenchyma cells from the pumpkin tissue exhibited collapses and separations, especially for Butternut. This species showed a lower hardness than Delica at time 0. For both species, 400MPa and thermal treatment were the most effective in the inactivation of pectinmethylesterase, which reactivated after 2 months, especially for Butternut. Colorimetric parameters decreased after all treatments. Antioxidant activity resulted affected by pressure, showing a significant increase during storage especially for the samples treated at 200MPa after 2 months, comparable to the thermal treated ones. Among the tested treatments, 400MPa may be considered as the best option for the quality retention during storage

Inulin-based emulsion filled gel as fat replacer in shortbread cookies: Effects during storage

Shortbread cookies with 0, 20, 40 and 50% fat replacement were obtained using an emulsion filled gel (EFG) based on inulin and extra virgin olive oil and studied during 60 storage days. Increasing the amount of EFG in shortbread cookies, higher volumes and harder texture were observed, in relation to the higher water availability and the lower fat content. Thermal analysis conducted by means of DSC and 1H-NMR confirmed the key role of lipids and water status on the mechanical properties of shortbread cookies. Darker colour and toasted notes were registered for increasing levels of EFG, in relation to the presence of inulin involved in the Maillard reaction. During storage, all the cookies resulted very stable regarding dimensions, colour and rancidity perception; only slight texture changes were observed, probably related to the moisture redistribution among the cookies components. EFG can be proposed as valuable ingredient to replace fats in shortbread cookies, allowing the use of the health claim “reduced saturated fat content” already from 40% butter substitution

Physical and Thermal Evaluation of Olive Oils from Minor Italian Cultivars

Authentication of extra virgin olive oils is a key strategy for their valorization and a way to preserve olive biodiversity. Physical and thermal analysis have been proposed in this study as fast and green techniques to reach this goal. Thirteen extra virgin olive oils (EVOOs) obtained from minor olive cultivars, harvested at three different ripening stages, in four Italian regions (Abruzzo, Apulia, Sardinia, and Calabria) have been studied. Thermal properties, viscosity and color, as influenced by fatty acid composition and chlorophyll content, have been investigated. The thermal curves of EVOOs, obtained by differential scanning calorimetry, were mostly influenced by the oleic acid content: a direct correlation with the cooling and heating enthalpy and an indirect correlation with the cooling transition range were observed. The minor fatty acids, and particularly arachidic acid, showed an influence, mostly on the heating thermograms. Viscosity and color showed respectively a correlation with fatty acids composition and chlorophyll content, however they didn’t result able to discriminate between the samples. Thanks to the principal component analysis, the most influencing thermal parameters and fatty acids were used to cluster the samples, based on their botanical and geographical origin, resulting instead the harvesting time a less influential variable

High pressure and thermal processing on the quality of zucchini slices

AbstractIn response to the market demand for low processed vegetables, high-pressure treatments (400,600 MPa; 1,5 min) were applied on zucchini slices and compared to a traditional blanching treatment. Histological observations, texture and color analysis, pectinmethylesterase (PME) and antioxidant (DPPH) activities were measured and compared to untreated samples. The histological observations revealed that the longer high-pressure treatments (5 min) led to more extended cell lysis and dehydration than the shorter ones (1 min) and blanching. High-pressure treatments resulted less effective than blanching on PME inactivation, with the best results obtained at 400 MPa for 1 min. Comparable texture parameters were observed for high-pressured and blanched samples. The negative correlation found between PME activity and the texture parameter 'distance of the first peak force' revealed an effect of PME on the texture recovery after treatments. High pressure led to a general browning of zucchini parenchyma and to DPPH drop. The correlations found between DPPH and color suggest the common nature of the phenomena. The influence of pressure and time on the studied parameters was revealed by two-way ANOVA. Principal component analysis clustered together the four high-pressure-treated samples, being clearly divided by blanched and untreated ones

Total phenolic content, antioxidative and antidiabetic properties of coconut (Cocos Nucifera L.) testa and selected bean seed coats

Natural alternatives for the treatment of diabetes mellitus have been the interest of many researchers. In this study, the brown testas of mature coconuts were compared to beans seed coats of four varieties in terms of antioxidative and anti-hyperglycaemic properties. The total phenolic and flavonoid contents, the antioxidant potentials and the α-amylase and α-glucosidase inhibitory activities of the crude extracts were studied in vitro. The results showed that extracts of coconut testa and red kidney bean seed coat displayed higher α-glucosidase inhibition (IC50=19.90±5.67 and 4.84±1.43 µg/ml) and α-amylase inhibition (IC50=120.5±15.4 and 532.8±68.0 µg/ml) than the other extracts. These two extracts showed higher antioxidant capacities owing to their high phenolic and flavonoid contents. These results suggest that red kidney bean seed coat and coconut testa would have higher potential as nutraceuticals and could serve as natural alternative sources of anti-diabetic remedy

Comparison of physical, microstructural and antioxidative properties of pumpkin cubes cooked by conventional, vacuum cooking and sous vide methods

BACKGROUND Current dietary guidelines recommend five or more fruit, vegetable, and legume servings per day. Often, these products are eaten cooked, resulting in organoleptic and nutritional changes. Vacuum cooking is gaining attention as an alternative cooking technique, due to its ability to preserve or even enhance sensory and healthy properties of food. Its household application is, however, poorly explored. In this work, the effect of vacuum cooking, performed with a new patented system, was studied for the first time on pumpkin cubes and compared to sous vide and traditional steam cooking, through a multidisciplinary approach. RESULTS All the cooking treatments damaged pumpkin microstructure, leading to cell separation and plasmolysis; vacuum cooking was the most aggressive method, as confirmed by texture softening. Vacuum cooking was also the method with less impact on pumpkin color, in relation to the largest extraction of some classes of carotenoids from the broken cells. Significant polyphenol extraction, especially of gallic acid and naringenin, was instead observed for sous vide and steamed pumpkins. The total antioxidant activity, ascribable to the effect of both carotenoids and polyphenols, resulted enhanced after cooking compared to raw one mainly for cook vide samples, followed by steamed and sous vide ones. CONCLUSIONS Vacuum cooking, followed by sous vide, has often shown better performance than traditional steam cooking for pumpkin cubes. The implementation of sous vide and vacuum cooking at domestic level or in professional kitchens, and in the food industry, would allow the consumption of vegetables with improved nutritional and sensorial characteristics. © 2020 Society of Chemical Industr