Calorimetry and thermal analysis in food science : an updated review

Food science is a domain of life science. Applications of thermal analysis and calorimetry (TAC) to food products deal with many investigation targets spanning from the characterization of the systems at molecular and supramolecular level to the description of the microbial metabolism. Food products are multi-phase and multi-component metastable systems where several processes can occur simultaneously during the preparation process and the shelf life. One therefore has to disentangle various contributions to the overall instrumental outputs, using appropriate data treatments and kinetic models, and/or results from other experimental approaches. The paper reports an updated survey of TAC applications to food products through specific examples of data treatments

Dissecting the effects of free fatty acids on the thermodynamic stability of complex model membranes mimicking insulin secretory granules

A stepwise micro-DSC study of Small, Large and Giant Unilamellar Vesicles prepared as pure and mixed systems of DMPC, DPPC, DSPC and DOPC was performed, achieving the preparation of final model membranes whose phospholipid compositions represent the 75% in terms of the phospholipids tails and the 50% headgroups of the Insulin Secretory Granules (vesicles located in the pancreatic Langerhans \u3b2-cells and which are responsible for insulin and amylin storage and secretion in response to nutrient intake). Moreover, the effect of Free Fatty Acids, whose levels are recurrently altered in diabetic and/or obese subjects, on the thermodynamic stability of the final membranes was eventually investigated. The results allowed to discriminate each single thermodynamic contribution among the main factors that dictate the overall thermodynamic stability of these complex unilamellar systems evidencing mainly entropic effects hierarchically summarized as phospholipid unsaturations > phospholipid tail length > membrane curvature. The effect of the Free Fatty Acids highlighted a strong stabilizing effect on the membranes as well as more pronounced phase segregations in the case of saturated acids (palmitic and stearic), whereas the opposite effect was observed in the case of an unsaturated one (oleic)

Water activity in biological systems. A review

Water deserves a major attention by researchers dealing with biological systems and related materials, like food, since it is ubiquitous and can be used like a \u201cnative\u201d probe to garner information about the hosting system, provided it may be freely displaced across. Its thermodynamic potential, namely, the water activity, aW, is related to that of the other compounds of the system considered via the Gibbs-Duhem relationship refl ecting the extent of the residual availability of water to solvate further solutes and sustain the molecular mobility of the bio-polymeric compounds. As for the experimental approaches to aW, this short review re-addresses the reader to other publications, while devotes a section to the Knudsen thermo-gravimetry that was used by the authors to determine the desorption isotherms of many food systems and related aqueous compounds. The paper remarks the importance of a preliminary assessment of water mobility and recalls the concept of \u201ccritical aW\u201c that takes into account the reduced mobility of water molecules in the vicinity of the glass transition. This opens the question of the reliability of sorption isotherms which encompass a wide aW range and the interpretation of the observed adsorption/desorption hysteresis. The multi-phase character of many biological systems is another issue of interest related to the reliability of the experimental approaches to aW. As examples of the role of aW on the stability of bio-systems and on the practice of a technological treatment, protein unfolding and osmo-dehydration of fruit pulps are reported

Isothermal calorimetry protocols to monitor the shelf life and aftermarket follow-up of fresh cut vegetables

Protocols and guidelines were assessed in order to apply isothermal calorimetry as a complementary/alternative method to monitoring, during the shelf life and the microbial growth/metabolism in commercial fresh cut vegetables with random initial microbial population. Moreover, the endogenous microbial population was used as a biosensor to check the modifications occurred during long storage for aftermarket characterization in the frame of vegetable waste treatments. Validation was obtained following ready-to-use carrots highlighting the effects of the different exposed surfaces (cylinders, sticks and a`-la-julienne cut) on the overall spoiling process during shelf life and green salad stored up to 14 days with regard to the aftermarket characterization

Thermogenic flux induced by lignoceric acid in peroxisomes isolated from HepG2 cells and from X- adrenoleukodystrophy and control fibroblasts

This work analyzes the thermogenic flux induced by the very long-chain fatty acid (VLCFA) lignoceric acid (C24:0) in isolated peroxisomes. Specific metabolic alterations of peroxisomes are related to a variety of disorders, the most frequent one being the neurodegenerative inherited disease X-linked adrenoleukodystrophy (X-ALD). A peroxisomal transport protein is mutated in this disorder. Due to reduced catabolism and enhanced fatty acid elongation, VLCFA accumulate in plasma and in all tissues, contributing to the clinical manifestations of this disorder. During peroxisomal metabolism, heat is produced but it is considered lost. Instead, it is a form of energy that could play a role in molecular mechanisms of this pathology and other neurodegenerative disorders. The thermogenic flux induced by lignoceric acid (C24:0) was estimated by isothermal titration calorimetry in peroxisomes isolated from HepG2 cells and from fibroblasts obtained from X-linked adrenoleukodystrophy patients and healthy subjects. Heat flux induced by lignoceric acid in HepG2 peroxisomes was exothermic, indicating normal peroxisomal metabolism. In X-ALD peroxisomes the heat flux was endothermic, indicating the requirement of heat/energy, possibly for cellular metabolism. In fibroblasts from healthy subjects the effect was less pronounced than in HepG2, a kind of cell known to have greater FA metabolism than fibroblasts. Our hypothesis is that heat is not lost but it could act a s an activator, for example on the heat-sensitive pathway related to TRVP2 receptors. To investigate this hypothesis we focused on peroxisomal metabolism, considering that impaired heat generation could contribute to the development of peroxisomal neurodegenerative disorders

Knudsen thermogravimetry approach to the thermodynamics of aqueous solutions

The use of isothermal TGA with Knudsen-like cells allows determination ofthe thermodynamic activity of water, aW. The typical experiment implies aslow dehydration ofthe aqueous solution atconstant temperature in dynamic vacuum conditions.The method isalternative to the classical isopiestic approach and offers the advantage ofacontinuous record onincreasing the solute concentration.These data can be directly treated according tothe classical thermodynamic relationships drawn from the Gibbs\u2013Duhem expression to evaluate the activity and osmotic coefficientofthe aqueous solutions ofelectrolytes and non-electrolytes, and,inthe case ofelectrolytes,allow determination ofsolubility ofthe solute.Discrepancies with respect to the literature data are observed when the viscosity ofthe systems becomes too high, asinthe case ofsugars with avery large solubility.Such amismatch may however beaccounted for either slowing the dehydration rate with use ofanarrower Knudsen orifice,orcorrecting the experimental aW with a calibration curve. The same approach can beapp lied tonon-aqueous solutions

Metabolic risk of new food technologies: calorimetric study of model cell membranes for the determination of the influence of free fatty acids (FFA) in diabetes mellitus onset

Type 2 diabetes mellitus (T2DM) is a chronic disease that continues to spread in both developed and developing countries. Indeed, the individuals affected by diabetes mellitus (type 1 and type 2) in the world are now close to 400 million and estimates suggest that they will reach 600 million by 2035. The rapid spreading of this disorder is influenced not only by genetic factors but also by environmental ones: socio-economic variations, evolution of lifestyle and changes in dietary habits have contributed to increase the percentage of overweight and obese individuals, which in turn have led to a greater diffusion of diabetes. In fact, weight gain is closely related to insulin-resistance onset, which is considered as the starting point for the development of the disease. However, the manner in which obesity and nutrition factors are linked to the onset of T2DM is not fully understood yet, especially at a molecular level. The aim of the project presented here is to prepare and characterize (thermodynamically and spectroscopically) model membranes which simulate as possible the phospholipid bilayers of the Langerhans \u3b2-cells in order to highlight and discriminate the role of the lipid composition and foodborne stress (in terms of [Ca2+] and [FFA]) in the membrane stability. Moreover, the interaction between the model membrane and hIAPP, which seems to be involved in \u3b2-cells death, will be used to evaluate the influence of membrane stability on T2DM onset

Thermodynamic stability of complex model membranes: the role of composition, morphology and food fatty acids

Free Fatty Acids (FFAs) have been shown to be involved in several membrane-mediated cellular processes as lipid-assisted protein transport across the bilayer, fusion of lipid vesicles/cells and signalling for several cell mechanisms (e.g. insulin secretion). However, altered plasma FFAs levels typical of obese and/or diabetic subjects have been proposed to contribute to the onset and progression of type 2 diabetes mellitus through both their possible involvement in altered metabolic pathways and their direct action on cell membranes. Moreover, the action of FFAs has also been hypothesized to play a role in the interaction of amylin, an amyloidogenic protein, with cell membranes likely leading to the pancreatic \u3b2-cells failure by apoptosis. Among several studies highlighting the FFAs-membrane interaction by means of spectroscopic, imaging, molecular dynamics and/or theoretical approaches, few works are devoted to a thermodynamic characterization of the role of FFAs on the overall membrane stability, however without considering the compositional and morphological complexity of real biological vesicles. In such a frame, the present work was aimed at the calorimetric investigation of small, large and giant unilamellar vesicles prepared as pure and mixed systems of phospholipids with different length and unsaturation level. The preparation of a final model membrane was finally achieved mimicking the phospholipid bilayer of Insulin Secretory Granules (ISGs), vesicles located in the pancreatic Langerhans \u3b2-cells and which are responsible for insulin and amylin storage and secretion in response to nutrients intake. This study was performed through micro-DSC and allowed to discriminate each single thermodynamic contribution among the main factors that dictate the overall thermodynamic stability of these complex unilamellar systems (phospholipid unsaturations > phospholipid tail length > membrane curvature). The effect of three different FFAs, such as palmitic, stearic and oleic acids, added in different percentages both to a completely saturated ternary model membrane and to an unsaturated one (i.e. the final model membrane made by the saturated one including the 5% of 1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC) was eventually investigated highlighting a strong stabilizing effect as well as more pronounced phase segregations in the case of saturated acids, whereas the opposite effect was observed in the case of unsaturated FFAs. Moreover, the stabilizing effects deriving from saturated FFAs were more pronounced in less stable membranes, i.e. the unsaturated one, whereas the destabilizing effects deriving from the unsaturated FFAs were more pronounced in more stable membranes, i.e. the completely saturated one

The DSC monitoring of oil melting to follow the oil curing

The drying of an oil paint is due to the polyunsaturations of the oil in the binder. Polyunsaturated oils dry trough an autoxidation process in which the double bonds of linolenic and linoleic acids naturally react with the oxygen present in the atmosphere. The gradual conversion of the liquid oil through a soft gel to a rubbery solid occurs as a result of a multistep free radical chain reaction. During the propagation step, hydroperoxides are formed. A method frequently used to follow the oil curing is the DSC monitoring of the peroxide decomposition peak during time. Since the oil polymerization affects its crystallinity, we propose here an altemative method to asses the oil curing. The melting peak of linseed oil samples is measured at different times of curing and compared with the pro\ufb01le of the peroxide decomposition peak over time. The comparison shows that the two phenomena are strongly correlated and that, when the maximum of the peroxide content is reached, the melting peak disappears. The study of the DSC melting peak is therefore proposed as a valid alternative tool to monitor the curing of an oil paint

Qualification of tumour mutational burden by targeted next-generation sequencing as a biomarker in hepatocellular carcinoma

Background & Aims: Tumour mutational burden (TMB) predicts improved response and survival to immunotherapy. In this pilot study, we optimized targeted next-generation sequencing (tNGS) to estimate TMB in hepatocellular carcinoma (HCC). Methods: We sequenced 48 non-paired samples (21 fresh-frozen [FF] and 27 paraffin-embedded [FFPE]), among which 11 FFPE samples were pretreated with uracil-DNA glycosylase (UDG). Thirty samples satisfied post-sequencing quality control. High/low TMB was defined by median number of mutations/Mb (Mut/Mb), across different minimum allele frequency (MAF) thresholds ( 650.05, 650.1 and 650.2). Results: Eligible patients (n\ua0=\ua029) were cirrhotic (84%) with TNM stage I-II HCC (75%). FFPE samples had higher TMB (median 958.39 vs 2.51 Mut/Mb, P\ua0\ua0T transitions at CpG sites (median 60.3% vs 9.1%, P\ua0=.002) compared to FF. UDG-treated samples had lower TMB (median 4019.92 vs 353 Mut/Mb, P\ua0=.041) and deamination counts (median 6393.5 vs 328.5, P\ua0=.041) vs untreated FFPE. At 0.2 MAF threshold with UDG treatment, median TMB was 5.48 (range 1.68-16.07) and did not correlate with salient pathologic features of HCC, including survival. Conclusion: While tNGS on fresh HCC samples appears to be the optimal source of tumour DNA, the low median TMB values observed may limit the role of TMB as a predictor of response to immunotherapy in HCC