Application and optimisation of air-steam cooking on selected vegetables: impact on physical and antioxidant properties.

BACKGROUND: Several studies investigated the impact of different cooking techniques on the quality of vegetables. However, the use of the combined air-steam cooking is still scarcely debated, despite the advantages informally referred by professional catering workers. In this study, its optimisation was studied on Brussels sprouts and pumpkin cubes to obtain the best physical (texture, colour) and antioxidant (FRAP, total phenols) response, in comparison to a conventional steaming treatment. RESULTS: Increasing the strength of the air-steam treatment, Brussels sprouts resulted to be softer, less green (higher a* value), richer in phenols and exhibited lower FRAP values than the steamed ones. The air-steamed pumpkin cubes exhibited an equivalent softening degree to that of steamed ones and, under the strongest cooking conditions, a higher antioxidant quality and a yellow darkening (lower b* value). Varying the cooking time and/or temperature, a linear change of force/compression hardness and a* (negative a*: greenness) for Brussels sprouts, b* (yellowness) and total phenol content for pumpkin cubes was observed. A predictive model for these variables was obtained by response surface methodology. The best process conditions to achieve the optimal desirability were also identified. CONCLUSION: The application of air-steam cooking under suitable time/temperature conditions could be proposed as an alternative method to a traditional steam cooking on Brussels sprouts and pumpkin cubes, being able to preserve or improve their quality. The best air-steam cooking conditions were 25 min at 90 °C for Brussels sprouts and 10 min at 110 °C for pumpkin. © 2017 Society of Chemical Industry.

Short-term storage evaluation of quality and antioxidant capacity in chestnut-wheat bread.

BACKGROUND: Bread traditionally made from wheat is now often supplemented with alternative functional ingredients as chestnut flours; no data have been previously published about the staling of chestnut-containing bread. Thus short-term storage (3 days) for chestnut flour-supplemented soft wheat bread is evaluated by means of selected physicochemical properties (i.e. water dynamics, texture, colour, crumb grain characteristic, total antioxidant capacity). RESULTS: Bread prepared with a 20:80 ratio of chestnut:soft wheat flours maintained its moisture content in both crust and crumb. Crumb hardness, after baking, was found to be significantly higher than that of the soft wheat bread; it did not change during storage, whereas it significantly increased in the control bread until the end of the shelf life. The supplemented bread presented a heterogeneous crumb structure, with a significant decrease in the largest pores during shelf life, relative to the shrinkage of crumb grain. The control exhibited a significant redistribution of crumb holes, with a decrease in the smallest grain classes and an increase in the intermediate ones, most likely caused by cell wall thickening. The colour of the crumb remained unaltered in both breads. The crust of the control presented a significant decrease of a* (redness) and that of the supplemented bread exhibited a decrease of b* (yellowness). The antioxidant capacity was detected after day 1 of storage in the chestnut flour bread only. CONCLUSION: Chestnut flour supplementation could represent a feasible way of producing bread with improved characteristics, not only just after baking but also during shelf life.

Evaluation of iodine content and stability in recipes prepared with biofortified potatoes.

Iodine is an essential micronutrient of the human diet. Deficiency of iodine is diffused in many areas of the world and mild deficiency is present also in developed countries around Europe. Biofortification of vegetables could represent a better strategy with respect to iodized salt in order to increase iodine intake. The aim of this study was evaluating the stability of iodine, derived from biofortified potatoes, in the preparation process of three Italian typical dishes: dumplings, vegetable pie, and focaccia bread. The obtained results showed a good stability of iodine in cooking processes, in particular, during baking of focaccia bread. Significant losses of iodine were detected during boiling of dumplings and baking of vegetable pie. Although the different stability during the cooking processes, the three dishes maintained a good final content of iodine, ranging from the 33.3% to 52.7% of daily recommended intake in adults for individual serving size.

Stability of iodine during cooking: investigation on biofortified and not fortified vegetables.

Biofortification of food crops through fertilization and salt iodization are key strategies for the prevention and control of iodine deficiency disorder. However, considerable losses of iodine can occur during processing. In this study, the stability of iodine in biofortified potatoes, carrots and tomatoes was evaluated during different domestic cooking procedures, as this matter was poorly discussed in literature. The stability of iodized salt during baking and boiling of carrots and potatoes not fortified was also investigated. All the adopted cooking procedures have proven to be suitable to preserve the iodine content in biofortified vegetables. During boiling test with iodized salt, neither potatoes nor carrots were able to absorb iodine added with salt, probably owing to the losses occurred during cooking. On the contrary, baking test on potatoes has not caused a significant degradation of iodized salt, and no significant differences in iodine concentration were detected before and after cooking.

Thermal and chemical evaluation of naturally auto-oxidised virgin olive oils: a correlation study.

BACKGROUND: The nature of the relationship between differential scanning calorimetry thermal properties and the oxidation and hydrolysis compounds formed during a real auto-oxidation process in virgin olive oils has not been evaluated so far, as these samples are difficult to find. In this work, 21 samples of virgin olive oil, stored under ideal conditions since their years of production (production range 1991-2005) to develop the natural auto-oxidation process, were analysed in order to evaluate this relationship. RESULTS: Oils stored the longest time showed the highest hydrolytic degradation while the others exhibited higher contents of oxidised fatty acids and triacylglycerols, instead. Thermal properties of transitions were differently influenced by degradation compounds with the onset of both the cooling and heating profiles particularly influenced by diacylglycerols and oxidised lipids. Chemical data and thermal properties were correlated by using principal component analysis. Twenty-three variables were selected for the analysis with the first component fully segregating samples into two groups according to the year of storage and the level of hydrolysis and/or oxidation, on the basis of selected thermal properties obtained by cooling and heating transitions. CONCLUSIONS: These preliminary findings showed that differential scanning calorimetry could be considered an useful tool to evaluate lipid degradation in virgin olive oils, indicating its value as a support to chemical techniques.

DSC evaluation of extra virgin olive oil stability under accelerated oxidative test: effect of fatty acid composition and phenol contents.

Three extra virgin olive oils having different fatty acid compositions and total phenol contents were submitted to an accelerated storage test at 60°C for up to 21 weeks. Their oxidative status, evaluated by peroxide values and total phenolic content, was related to differential scanning calorimetry cooling profiles and thermal properties. Changes in crystallization profiles were consistent starting from 12 weeks for the two oil samples (B and C) that had a higher content of linoleic acid and medium/low amounts of phenols, respectively, whereas they became detectable at the end of the test for the remaining oil (sample A). Decrease of crystallization enthalpy and shift of transition towards lower temperature were also evident at 4 weeks of storage for samples B and C, whereas the same changes in the transition profile were noticeable at 12 weeks for sample A. Differential scanning calorimetry appears to be suitable for the discrimination of oxidative status of extra virgin olive oils with widely different fatty acid composition.

Differential scanning calorimetry thermal properties and oxidative stability indices of microwave heated extra virgin olive oils.

BACKGROUND: The use of differential scanning calorimetry (DSC) for assessing the deterioration effect of microwave heating on vegetable oils, and on olive oils in particular, has been partially explored in literature. The aim of this work was to evaluate the potential of DSC to discriminate among microwaved extra virgin olive oils (EvOo from different olive cultivar and origin), according to changes on thermal properties (upon cooling and heating) and traditional oxidative stability indices (peroxide, p-anisidine and TOTOX values). RESULTS: An elevated value of lipid oxidation was reached by the most unsaturated EvOo sample (9.5% of linoleic acid) at 6 min of microwave treatment. Free acidity significantly increased (0.42%) only for the oil sample with the highest water content (874 mg kg(-1) oil) at the longest time of treatment. Crystallisation enthalpies significantly decreased and the major exothermic peak shifted towards lower temperature, leading to enlargement of the transition range in all samples due to the formation of weak and mixed crystals among triacylglycerols and lipid degradation products. On the contrary, thermal properties upon heating appeared to similarly vary among samples. CONCLUSIONS: The analysis of DSC thermal properties upon cooling seemed to clearly discriminate among different EvOo samples after microwaving. The relation between changes of thermal properties and oxidation parameters should be further studied using additional oxidative stability indices on a larger set of oil samples, due to the complexity of EvOo composition.

Study on the effects of heating of virgin olive oil blended with mildly deodorized olive oil: focus on the hydrolytic and oxidative state.

In this study, mildly deodorized olive oil (DEO) and its admixtures with extra virgin olive oil (EVOO) have been analyzed after heating treatments by microwave and conventional oven. Different patterns in oxidative and hydrolytic degradation of lipids in genuine and sophisticated olive oils have been evaluated by chromatographic and spectroscopic methods and related to heating treatments. The experimental plan focused on the assessment of the (a) hydrolytic degree of the samples by the free acidity and the 1,2- and 1,3-diacylglycerols (DAG) determinations; (b) oxidative status of the samples by the assessment of the peroxide value (POV) and oxidized fatty acid (OFA), the specific absorption at 270 nm (k(270)), the accelerated aging test (OSI) and volatile compounds. In general, the thermal treatment by conventional oven led to a higher content of 1,3-DAG and secondary oxidation products than microwave heating. A duo-trio sensory test was also performed: tasters were not able to discriminate between EVOO and DEO heated by conventional oven whereas they were when oils were microwaved.

Study of chemical changes produced in virgin olive oils with different phenolic contents during an accelerated storage treatment.

Chemical changes produced in an extra virgin olive oil sample in the presence (EVOO) and absence (EVOOP) of its phenolic fraction during an accelerated storage treatment at 60 degrees C up to 7 weeks were studied. Modifications in phenol content, as well as changes in several quality parameters (free acidity, peroxide value, UV absorbance, fatty acid composition, oxidative stability index, and tocopherol content) were also evaluated under the same storage conditions and compared to those of the same sample deprived of phenolic compounds. When the phenolic extract of the EVOO was studied, a decrease of the antioxidants first present in the sample and an increase of the oxidized products were observed. In addition, oxidation seemed to produce the transformation of such phenolic compounds as secoiridoids and the appearance of oxidized forms of them. These latter compounds could be used as molecular markers of the lack of extra virgin olive oil freshness.

Thermal decomposition study of monovarietal extra virgin olive oil by simultaneous thermogravimetry/differential scanning calorimetry: relation with chemical composition.

Thermal decomposition of 12 monovarietal extra virgin olive oils from different geographical origins (eight from Italy, two from Spain, and the others from Tunisia) was evaluated by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses. All extra virgin olive oils showed a complex multistep decomposition pattern with the first step that exhibited a quite different profile among samples. Thermal properties of the two peaks obtained by the deconvolution of the first step of decomposition by DSC were related to the chemical composition of the samples (triacylglycerols, fatty acids, total phenols and antioxidant activity). Onset temperatures of the thermal decomposition transition and T(p) values of both deconvoluted peaks as well as the sum of enthalpy were found to exhibit statistically significant correlations with chemical components of the samples, in particular palmitic and oleic acids and related triacylglycerols. Activation energy values of the second deconvoluted peak obtained by the application of kinetic procedure to the first step of decomposition were also found to be highly statistically correlated to the chemical composition, and a stability scale among samples was proposed on the basis of its values.

Differential scanning calorimetry: a potential tool for discrimination of olive oil commercial categories.

Differential scanning calorimetry thermograms of five commercial categories of olive oils (extra virgin olive oil, olive oil, refined olive oil, olive-pomace oil and refined olive-pomace oil) were performed in both cooling and heating regimes. Overlapping transitions were resolved by deconvolution analysis and all thermal properties were related to major (triacylglycerols, total fatty acids) and minor (diacylglycerols, lipid oxidation products) chemical components. All oils showed two well distinguishable exothermic events upon cooling. Crystallization enthalpies were significantly lower in olive oils due to a more ordered crystal structure, which may be related to the higher triolein content. Pomace oils exhibited a significantly higher crystallization onset temperature and a larger transition range, possibly associated to the higher amount of diacylglycerols. Heating thermograms were more complex: all oils exhibited complex exo- and endothermic transitions that could differentiate samples especially with respect to the highest temperature endotherm. These preliminary results suggest that both cooling and heating thermograms obtained by means of differential scanning calorimetry may be useful for discriminating among olive oils of different commercial categories.

Monovarietal extra virgin olive oils. Correlation between thermal properties and chemical composition: heating thermograms.

Extra virgin olive oils from drupes of three Sicilian varieties (Biancolilla, Cerasuola, and Nocellara del Belice) collected at three different harvesting periods were analyzed upon heating by means of DSC, and thermal properties were related to the chemical composition of the samples. All thermograms exhibited multiple transitions with a minor exothermic peak, followed by a major endothermic event. Cerasuola samples showed higher overall enthalpy and narrower range of transition at all harvesting periods, as compared to the other oils. A more ordered crystal structure originating from a more uniform chemical composition, with higher triolein content, in Cerasuola may be hypothesized. At different harvesting periods, thermal transitions started at lower temperatures and developed over a narrower range in all cultivars, probably due to the insertion of molecules derived from triacylglycerol lysis (diacylglycerols and free fatty acids) and lipid oxidation products into the triacylglycerol crystal lattice. All heating thermograms were deconvoluted into one exothermic and five endothermic constituent peaks, and the effect of chemical components on thermal properties of the peaks was evaluated. DSC application upon heating appears to be very promising in discriminating among oil samples from olives of different cultivars and/or harvesting periods.

Monovarietal extra virgin olive oils: correlation between thermal properties and chemical composition.

Thermal properties of monovarietal extra virgin olive oils were evaluated by means of differential scanning calorimetry (upon cooling) and related to their chemical composition (triacylglycerols, diacylglycerols, total and free fatty acids, oxidation status). The overall crystallization enthalpy did not significantly differ among samples and did not account for the differences observed in chemical compositions. On the contrary, a higher degree of unsaturation in the lipid profile induced a shift of the crystallization onset towards lower temperatures and narrowing of the crystallization temperature range. The presence of triacylglycerol lysis and lipid oxidation products shifted the crystallization towards higher temperatures and the phase transition developed over a larger temperature range. Differential scanning calorimetry thermograms were deconvoluted into three constituent exothermic peaks for all samples. The area of the two lower-temperature exotherms was found to be statistically correlated with the amount of triunsaturated and monosaturated triacylglycerols present in the oil. Thermal properties of extra virgin olive oil were found to be affected by oil chemical composition.