Farm to Fork Stability of Phytochemicals and Micronutrients in Brassica oleracea and Allium Vegetables.

Brassica oleracea and Allium vegetables are known for their unique, family specific, water-soluble phytochemicals, glucosinolates, and S-alk(en)yl-l-cysteine sulfoxides, respectively. However, they are also important delivery systems of several other health-related compounds, such as carotenoids (lipid-soluble phytochemicals), vitamin C (water-soluble micronutrient), and vitamin K1 (lipid-soluble micronutrient). When all-year-round availability or transport over long distances is targeted for these often seasonal, locally grown vegetables, processing becomes indispensable. However, the vegetable processing chain, which consists of multiple steps (e.g., pretreatment, preservation, storage, preparation), can impact the nutritional quality of these vegetables corresponding to the nature of the health-related compounds and their susceptibility to (bio)chemical conversions. Since information about the impact of the vegetable processing chain is scattered per compound or processing step, this review targets an integration of the state of the art and discusses needs for future research. Starting with a discussion on substrate-enzyme location within the vegetable matrix, an overview is provided of the impact and potential of processing, encompassing a wide range of (nonenzymatic) conversions.

Stability and bioaccessibility of micronutrients and phytochemicals present in processed leek and Brussels sprouts during static in vitro digestion.

Vegetables are frequently processed before consumption. However, vegetable functionalization continues beyond ingestion as the human digestive tract exposes vegetable products to various conditions (e.g. elevated temperature, pH alterations, enzymes, electrolytes, mechanical disintegration) which can affect the stability of micronutrients and phytochemicals. Besides the extent to which these compounds withstand the challenges posed by digestive conditions, it is equally important to consider their accessibility for potential absorption by the body. Therefore, this study investigated the impact of static in vitro digestion on the stability (i.e. concentration) and bioaccessibility of vitamin C, vitamin K1, glucosinolates, S-alk(en)yl-l-cysteine sulfoxides (ACSOs) and carotenoids in Brussels sprouts (Brassica oleracea var. gemmifera) and leek (Allium ampeloprasum var. porrum). Water-soluble compounds, glucosinolates and ACSOs, remained stable during digestion while vitamin C decreased by >48%. However, all water-soluble compounds were completely bioaccessible. Lipid-soluble compounds were also stable during digestion but were only bioaccessible for 26-81%.

Impact of refrigerated storage on (bio)chemical conversions of health-related compounds in pretreated, pasteurized Brussels sprouts and leek.

Vegetable processing often consists of multiple processing steps. Research mostly focused on the impact of individual processing steps on individual health-related compounds. However, there is a need for more holistic approaches to understand the overall impact of the processing chain on the health potential of vegetables. Therefore, this work studied the impact of pretreatment (relatively intact versus pureed vegetable systems), pasteurization and subsequent refrigerated storage (kinetic evaluation) on multiple health-related compounds (vitamin C, vitamin K1, carotenoids, glucosinolates and S-alk(en)yl-L-cysteine sulfoxides (ACSOs)) in Brussels sprouts and leek. It could be shown that differences introduced by different types of pretreatment were not nullified during pasteurization and refrigerated storage. Clearly, enzymatic conversions controlled during pretreatment resulted in different health-related compound profiles still observable after pasteurization. Moreover, about -42% and -100% relative concentration differences of ACSOs and dehydroascorbic acid, respectively, were detected immediately after pasteurization, while glucosinolates concentrations decreased by about 47% during refrigerated storage. All other compounds were stable during pasteurization and refrigerated storage.

Barriers impairing mineral bioaccessibility and bioavailability in plant-based foods and the perspectives for food processing.

Plant-based foods gain more importance since they play a key role in sustainable, low-meat and healthy diets. In developing countries, these food products, especially legumes and cereals, are important staple foods. Nevertheless, the question arises on how efficient they are to deliver minerals and if it is useful to encourage their consumption to reduce the prevalence of mineral deficiencies? This review paper focuses on the discrepancy between the mineral content and the amount of minerals that can be released and absorbed from plant-based foods during human digestion which can be attributed to several inherent factors such as the presence of mineral antinutrients (phytic acid, polyphenols and dietary fiber) and physical barriers (surrounding macronutrients and cell wall). Further, this review paper summarizes the effects of different processing techniques (milling, soaking, dehulling, fermentation, germination and thermal processing) on mineral bioaccessibility and bioavailability of plant-based foods. The positive impact of these techniques mostly relies on the fact that antinutrients levels are reduced due to removal of fractions rich in antinutrients and/or due to their leaching into the processing liquid. Although processing can have a positive effect, it also can induce leaching out of minerals and a reduced mineral bioaccessibility and bioavailability.

Structurally modified pectin for targeted lipid antioxidant capacity in linseed/sunflower oil-in-water emulsions.

The present work explored the lipid antioxidant capacity of citrus pectin addition to 5%(w/v) linseed/sunflower oil emulsions stabilized with 0.5%(w/v) Tween 80, as affected by pectin molecular characteristics. The peroxide formation in the emulsions, containing tailored pectin structures, was studied during two weeks of storage at 35°C. Low demethylesterified pectin (≤33%) exhibited a higher antioxidant capacity than high demethylesterified pectin (≥58%), probably due to its higher chelating capacity of pro-oxidative metal ions (Fe2+), whereas the distribution pattern of methylesters along the pectin chain only slightly affected the antioxidant capacity. Nevertheless, pectin addition to the emulsions caused emulsion destabilization probably due to depletion or bridging effect, independent of the pectin structural characteristics. These results evidence the potential of structurally modified citrus pectin as a natural antioxidant in emulsions. However, optimal conditions for emulsion stability should be carefully selected.

Lycopene degradation and isomerization kinetics during thermal processing of an olive oil/tomato emulsion.

The stability of lycopene in an olive oil/tomato emulsion during thermal processing (80-140 °C) was studied. Initially, the degradation of total lycopene (all-E plus Z-forms) occurred quickly at temperatures above 100 °C. However, a nonzero plateau value, depending on the processing temperature, was attained after longer treatment times. Besides degradation, the isomerization of total-Z-lycopene as well as the individual isomerization of all-E-, 5-Z-, 9-Z-, and 13-Z-lycopene was studied in detail. After prolonged heating, the isomer conversion reached a temperature-dependent equilibrium state. The degradation of total lycopene and the isomerization could be described by a fractional conversion model. The temperature dependency of the corresponding reaction rate constants was quantified by the Arrhenius equation. The activation energy of degradation was estimated to be 28 kJ/mol, and the activation energy of overall (all-E and total-Z) isomerization was estimated to be 52 kJ/mol.

The kinetics of ß-elimination of cystine and the formation of lanthionine in gliadin.

When gliadin, a mixture of wheat storage proteins containing only intramolecular disulfide (SS) bonds, is heated at high temperatures and preferably at alkaline pH, the SS bonds are cleaved by ß-elimination reactions leading to decreased cystine levels and the generation of dehydroalanine (DHA) and free sulfhydryl (SH) groups. DHA and the free SH group of cysteine can further react to form the irreversible cross-link lanthionine (LAN). The kinetics of this reaction were studied by heating model systems containing gliadin at different pH values (pH 6.0, 8.0 and 11.0) at temperatures up to 120 °C. Multiresponse modeling was applied to simultaneously describe the course of the reaction partners, intermediates and products. The estimated kinetic parameters indicate that the reaction rate constant for the elimination reaction increases with temperature and pH. Moreover, the predominant reaction consuming the intermediary DHA is the cross-link with cysteine to form LAN following second-order reaction kinetics. The corresponding reaction rate constant is less dependent on temperature and pH. Use of the proposed kinetic model to estimate reaction product concentrations in cereal-based foods allowed us to conclude that the ß-elimination reaction may be less important during, e.g., bread making, but may well contribute to gluten network formation during the production of soft wheat products. It may also well be relevant in the production of bioplastics made from gluten.

Effect of amino acids on acrylamide formation and elimination kinetics.

The effect of amino acids other than asparagine on acrylamide (AA) formation/elimination kinetics was studied in an asparagine-glucose model system (0.01 M, pH 6) heated at temperatures between 140 and 200 degrees C. Addition of cysteine or lysine to the model significantly lowered the AA yield, whereas addition of glutamine had a strong promoting effect and of alanine a rather neutral effect on the AA formation. This was also reflected by AA formation/elimination kinetics, which for all model systems studied could be modeled by two consecutive first-order reactions. The ratio of the elimination to the formation rate constant increased from the systems to which glutamine or alanine was added, over the control model system, to the model systems that contained lysine or cysteine.