Extrusion processing of pure chokeberry (Aronia melanocarpa) pomace: impact on dietary fiber profile and bioactive compounds

The partial substitution of starch with dietary fiber (DF) in extruded ready-to-eat texturized (RTE) cereals has been suggested as a strategy to reduce the high glycemic index of these food products. Here, we study the impact of extrusion processing on pure chokeberry (Aronia melanocarpa) pomace powder (CPP) rich in DF and polyphenols (PP) focusing on the content and profile of the DF fractions, stability of PP, and techno-functional properties of the extrudates. Using a co-rotating twin-screw extruder, different screw speeds were applied to CPP with different water contents (c$_{w}$), which resulted in specific mechanical energies (SME) in the range of 145–222 Whkg$^{-1}$ and material temperatures (T$_{M}$) in the range of 123–155 °C. High molecular weight soluble DF contents slightly increase with increasing thermomechanical stress up to 16.1 ± 0.8 g/100 g dm as compared to CPP (11.5 ± 1.2 g/100 g dm), but total DF (TDF) contents (58.6 ± 0.8 g/100 g dm) did not change. DF structural analysis revealed extrusion-based changes in the portions of pectic polysaccharides (type I rhamnogalacturonan) in the soluble and insoluble DF fractions. Contents of thermolabile anthocyanins decrease linearly with SME and temperature from 1.80 ± 0.09 g/100 g dm in CPP to 0.24 ± 0.06 g/100 g dm (222 Whkg$_{-1}$, 155 °C), but phenolic acids and flavonoids appear to be largely unaffected. Resulting techno-functional (water absorption and water solubility) and physical properties related to the sensory characteristics (expansion, hardness, and color) of pure CPP extrudates support the expectation that granulated CPP extrudates may be a suitable food ingredient rich in DF and PP

Impact of defined thermomechanical treatment on the structure and content of dietary fiber and the stability and bioaccessibility of polyphenols of chokeberry (Aronia melanocarpa) pomace

Dietary fiber is a potential replacement for other ingredients such as starch in reformulated extruded breakfast cereals. Analysis of chokeberry pomace powder revealed a total dietary fiber content of 57.8 ± 2 g/100 g with 76% being insoluble, 20% high molecular soluble and 4% low molecular soluble dietary fiber. The fiber polysaccharide composition was analyzed in detail by using a variety of analytical approaches. Extrusion-like processing conditions were studies in a Closed Cavity Rheometer enabling the application of defined thermal (temperature range 100–160 °C) and mechanical treatments (shear rates between 0.1 s$^{-1}$ and 50 s$^{-1}$) to chokeberry pomace powder. Application of temperatures up to 140 °C irrespective of the mechanical treatment does not remarkably alter dietary fiber structure or content, but reduces the initial content of total polyphenols by about 40% to a final content of 3.3 ± 0.5 g/100 g including 0.63 ± 0.1 g/100 g of anthocyanins, 0.18 ± 0.02 g/100 g of phenolic acids and 0.090 ± 0.007 g/100 g of flavonols, respectively. The retained polyphenols are fully bioaccessible after in vitro digestion, and antioxidant capacity remains unchanged as compared to the untreated pomace powder. Glucose bioaccessibility remains unaffected, whereas glucose content is reduced. It is concluded that chokeberry pomace powder is a good source of dietary fiber with the potential to partially substitute starch in extruded breakfast cereals

Effect of potassium fertilization on the contents of antioxidants in three cocktail tomato cultivars

Tomatoes are an important source of health beneficial phytochemicals, which act as antioxidants such as ascorbic acid, phenolic compounds, carotenoids, and tocopherols. The content of antioxidants is influenced, among others, by abiotic stress factors, like the nutritional status. Potassium (K) is a macronutrient, which is essential for several physiological functions in plants, for example, translocation of assimilates, activation of enzymes, maintenance of turgescence, and stomata regulation. The aim of this study was to investigate the effect of increasing K fertilization on the concentration of antioxidants in cocktail tomatoes. Therefore, three tomato cultivars (Primavera, Resi, and Yellow Submarine), grown in an outdoor pot experiment, were fertilized with increasing K doses for two consecutive years. It was confirmed that antioxidants in tomato fruit can be affected by the K regime, but was also shown that other factors may reduce or even inverse those effects when cultivation takes place in an uncontrolled outdoor environment. Most consistent K fertilization effects were found for naringenin, p-coumaric acid and caffeic acid. However, enrichment of tomatoes with antioxidants by K fertilization is cultivar dependent and, therefore, general statements should be avoided