Food Biomolecule Engineering by Unconventional Technological Strategies

openDriven by new consumers’ needs, over the last years, food processing shifted from the prior emphasis in process and unit operations to the design of products meeting specific requirements in terms of nutritional, biological and functional properties (tailor made foods). As food structure and functions are closely interlinked, structural changes of food constituents can lead to new product characteristics or improved functionalities. To this regard, different driving forces, such as mechanical or electromagnetic energy, were shown to effectively affect the structure of food proteins or polysaccharides. Taking advantage of specific potentials and opportunities of these unconventional technologies by focusing on the complex process-structure-function relationship, offers the exiting possibility for the development of fresh-like, healthy, tailor made foods. It is evident that this goal can only be reached by clearly understand the effects of the process on biomolecule structure and thus functions. In this context, this PhD thesis aimed to investigate whether and how unconventional technologies, such as light processing and high pressure homogenisation, can be exploited to modify biomolecule structure inducing changes in their own functions as well as in the functions of other bioactives present in the matrix. To this purpose, the thesis was divided in two parts. In the first part, the effect of UV-C and pulsed light on the structure and functions of selected proteins, including polyphenoloxidase (PPO), gluten, and egg white was investigated. In the second part, the effect of high pressure homogenisation on egg white proteins structure and functions as well as on microstructure and carotenoid bioaccessibility (BAc) of tomato pulps was studied. The first part of this PhD research focussed on the effects of light processing on selected proteins which serve important functionalities in foods. In particular, the effect of PL on the structure and enzymatic activity of PPO in model solution, the effect of UV-C light and PL on the structure and technological performances (viscosity, gelling and foaming properties) as well as immunoreactivity of egg white proteins, the effect of PL on wheat gluten structure and immunoreactivity, the effect of PL on wheat starch structure and gelatinization, and the effect of PL on wheat flour microstructure and immunoreactivity was studied. Light processing was found to modify protein structure thus leading to changes in protein functionalities. For instance, pulsed light promoted structural changes of PPO and egg white proteins by means of cleavage and aggregation/unfolding phenomena. The latter led to inactivation of PPO in model systems, better foaming properties but also higher immunoreactivity of egg white proteins. Besides, PL induced structural changes of gluten proteins by means of depolymerisation and unfolding phenomena, leading to the decrease in immunoreactivity of gluten proteins. By contrast, no changes in wheat starch structure and functions could be observed upon exposure to PL. Results relevant to the first part of this PhD thesis show that light processing, based on UV-C light or applied in a pulsed mode, on the one hand can be exploited as a sanitisation treatment without impairing starch performances, and on the other hand it can be regarded as a promising technology to modify protein structure and functions. However, the overall effects of light processing on food biopolymers depend on several factors: i) intrinsic photosensitivity of the target biomolecule (presence of light absorbing sites able to initiate photoreactions), ii) intensity of light radiation, iii) structural arrangement (intra- and inter-molecular interactions occurring , and iv) environmental conditions (crowding effect) experienced by the target biomolecule. These factors should be carefully considered when light processing is intended for modification of protein functionalities. The second part of this PhD research focussed on the effect of HPH processing on food biomolecules. To this aim two different matrices were chosen, namely egg white and tomato puree, as an example of protein- and polysaccharide-containing matrix. Results obtained show that HPH processing can be regarded as a promising technological strategy for improving the functional properties of both proteins and polysaccharides. In the case of egg white, HPH-induced modifications included the destruction of the original protein-protein interactions, protein unfolding, and formation of novel intramolecular interactions between unfolded proteins that resulted in the formation of a weak and unstable network. With regard to fibrous polysaccharides (cell wall polysaccharides in tomato), HPH promoted the interactions between fibres resulting in the formation of a network. The observed protein and polysaccharide structure modifications accounted for different function modifications. With regard to egg white proteins, structure modification did not impair the technological functionalities, but turned out to be sufficient to hide protein epitopes, leading to a slight decrease in egg white immunoreactivity. In the case of tomato pulps, if on the one hand the formation of structure in the food matrix could improve texture, stability and sensory attributes, on the other hand this structure could impair the bioavailability of micronutrients, such as carotenoids. In conclusion, results reported in this PhD thesis show that unconventional technologies, such as light and HPH processing represent promising technological strategies to fulfil the new consumers’ needs towards safe, fresh-like, healthier food products. The choice of the type of processing is driven by the nature of the biomolecule and the expected effect on its structure and functions. Protein and polysaccharide functions can be steered by choosing the proper process with adequate processing conditions. To this regard, the results of this thesis also suggest that the designing of the process should be carefully evaluated on a case by case basis, since undesired effects (i.e. increase in immunoreactivity of proteins or decrease in micronutrients bioaccessibility) may also occur under specific technological conditions. For this reason, understanding the mechanism that control the effect of the process on food structure and functions is crucial for engineering food biomolecule and obtaining foods with the desired characteristics.Dottorato di ricerca in Scienze degli alimentiopenPanozzo, Agnes

Effect of ultrasound treatment, oil addition and storage time on lycopene stability and in vitro bioaccessibility of tomato pulp

This study was performed to investigate the influence of ultrasound processing on tomato pulp containing no sunflower oil, or increasing amounts (i.e. 2.5%, 5% and 10%), on lycopene concentration and in vitro bioaccessibility at time zero and during storage at 5 \ub0C. Results confirmed previous findings in that ultrasonication was responsible for cell breakage and subsequent lycopene release in a highly viscous matrix. Neither the ultrasound process nor oil addition affected lycopene concentration. A decrease of approximately 35% lycopene content occurred at storage times longer than 15 days, due to isomerisation and oxidation reactions. No differences in lycopene in vitro bioaccessibility were found between the untreated and ultrasonically treated samples; this parameter decreased as a consequence of oil addition. Losses of lycopene in vitro bioaccessibility ranging between 50% and 80% occurred in the untreated and ultrasonically treated tomato pulps with and without oil during storage, mainly due to carotenoid degradation

Viscoelastic properties of high pressure homogenised citrus fibre fractions obtained after sequential pectin extraction

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Accelerated shelf life testing (ASLT) of oils by light and temperature exploitation

The peroxide formation rate was measured in sunflower and soybean oils exposed to increasing light intensity, from 0 to 8000 lx, at 10, 20 and 30 degrees C. Results indicated that shelf life estimation of photosensitive foods under actual or accelerated conditions cannot be correctly achieved if the effect of light is not taken into account. At each lighting level, the Arrhenius equation was applied to develop a model predicting oil shelf life. Thermal activation energy was lower than 50 kJ/mol, indicating temperature to be a scarcely efficient accelerating factor. In contrast, the oxidation rate was significantly affected by light according to a power law equation, whose parameters describe the electromagnetic activation energy of the reaction. The model accounting for the effect of light on oxidation rate was merged with the Arrhenius equation to get a model predicting shelf life on the basis of the concomitant changes in both temperature and light

Effect of pulsed light on selected properties of egg white

The effect of pulsed light (from 1.75 to 31.5 J cm- 2) on selected properties of egg white (absorbance, particle size, protein fractions, free sulfhydryl content, immunoreactivity, viscosity, gelling and foaming properties) was investigated. Pulsed light induced the development of browning, the formation of large protein aggregates by disulfide exchange, and protein backbone cleavage. These structural modifications cause an increase in immunoreactivity and a decrease in gelling temperature. However, no changes in viscosity and gel strength were observed. Egg white exposed to pulsed light produced foams with higher stability. This effect was attributed to jamming of protein aggregates and fragments in the fluid interstices between bubbles. Industrial relevance Pulsed light promotes structural changes of egg white proteins modifying their functional properties. Pulsed light treatment has a good potential for successful application in improving functional properties of protein rich ingredients. \ua9 2013 Elsevier Ltd. All rights reserved

Inactivation of Polyphenoloxidase by Pulsed Light

The effect of pulsed light on the inactivation of polyphenoloxidase (PPO) in model solutions was investigated focusing on the effect of enzyme concentration and total energy dose of the treatment. PPO inactivation increased with the dose of the treatment. Complete enzyme inactivation was achieved by pulsed light doses higher than 8.75 J cm-2. At low PPO concentrations (4 to 10 U), the enzyme resulted highly inactivated by pulsed light treatment. Further increase in enzyme units determined a progressive decrease in PPO inactivation. The latter was attributed to protein structural modifications including cleavage and unfolding/aggregation phenomena. PPO amounts higher than 10 U probably favoured enzyme conformations that were less prone to intermolecular rearrangements leading to inactivation. \ua9 2013 Institute of Food Technologists\uae

Effect of ultraviolet processing on selected properties of egg white

The effect of ultraviolet processing (10.6 and 63.7 kJ m-2) on selected properties of egg white (absorbance, particle size, protein fractions, free sulfhydryl content, immunoreactivity, viscosity, gelling and foaming properties) was investigated. Ultraviolet exposure induced the development of browning, the formation of large protein aggregates by disulfide exchange, and protein backbone cleavage. However, egg white proteins were differently sensitive to UV radiation. No changes in immunoreactivity, gelling temperature and gel firmness were observed. Independently on the UV dose, light treated egg white produced foams with higher stability. This effect was attributed to protein aggregates jamming in the fluid interstices between bubbles and/or to the higher viscosity of the aqueous phase. The latter was also associated to higher foam volume. \ua9 2012 Elsevier Ltd. All rights reserved

Carotenoid transfer to oil during thermal processing of low fat carrot and tomato particle based suspensions

Carotenoid solubilization in the oil phase is a prerequisite for carotenoid bioaccessibility during digestion. However, the level of bioencapsulation and the hydrophobicity of carotenoids were proven to strongly affect their transfer to oil during in vitro digestion. Therefore, thermal processing (95-110 °C) was exploited to favor carotenoid transfer from tomato- and carrot-based fractions to the oil before digestion. Initially, the total (all-trans+cis) carotenoid content in the oil increased quickly, thereafter, depending on the temperature applied, either a drop or a plateau was reached at longer treatment times. Treatment conditions of >100 °C for 10 min significantly favoured carotenoid transfer to oil (≥75 %). The rates of transfer to oil were as follows: β-carotene≈α-carotene>lycopene. The results revealed that the cell wall hinders carotenoid transfer to oil during thermal processing. Overall, the results indicate that typical high temperature short time thermal processing can be sufficient to achieve maximal carotenoid transfer to oil with minimal degradation in real food systems/food emulsions and this can be crucial to improve the nutritional quality of carrot and tomato based products.publisher: Elsevier articletitle: Carotenoid transfer to oil during thermal processing of low fat carrot and tomato particle based suspensions journaltitle: Food Research International articlelink: http://dx.doi.org/10.1016/j.foodres.2016.05.019 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe

Effect of pulsed light on structure and immunoreactivity of gluten

The effect of pulsed light (from 1.75 to 26.25 J cm(-2)) on selected properties of wheat gluten powder and aqueous suspension (absorbance, particle size and microstructure, free sulfhydryl content, protein fractions, protein electrophoretic mobility and immunoreactivity) was investigated. Gluten photoreactivity was strongly affected by hydration. While minor photo-induced structure modifications were observed in gluten powder, pulsed light induced the development of browning and promoted partial depolymerisation of hydrated gluten proteins by disulphide exchange. These changes were associated with a significant decrease in immunoreactivity, suggesting that pulsed light could be exploited to efficiently modify structure and thus functionality of gluten

Role of structural barriers in the in vitro bioaccessibility of anthocyanins in comparison with carotenoids

Although natural structural barriers are factors limiting nutrient bioaccessibility, their specific role in anthocyanin bioaccessibility is still unknown. To better understand how natural barriers govern bioactive compound bioaccessibility, an experimental approach comparing anthocyanins and carotenoids was designed, using a single plant matrix. Initial results revealed increased anthocyanin bioaccessibility in masticated black carrot. To explain this observation, samples with increasing levels of bioencapsulation (free-compound, homogenized-puree, puree) were examined. While carotenoid bioaccessibility was inversely proportional to the level of bioencapsulation, barrier disruption did not increase anthocyanin bioaccessibility. This means that mechanical processing is of particular importance in the case of carotenoid bioaccessibility. While micelle incorporation is the limiting factor for carotenoid bioaccessibility, anthocyanin degradation under alkaline conditions in the gastrointestinal tract dominates. In the absence of structural barriers, anthocyanin bioaccessibility is greater than that of carotenoids.publisher: Elsevier articletitle: Role of structural barriers in the in vitro bioaccessibility of anthocyanins in comparison with carotenoids journaltitle: Food Chemistry articlelink: http://dx.doi.org/10.1016/j.foodchem.2017.01.062 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved.status: publishe