High-Pressure Processing of Kale: Effects on the Extractability, In Vitro Bioaccessibility of Carotenoids & Vitamin E and the Lipophilic Antioxidant Capacity

Abstract

High pressure processing (HPP) represents a non-thermal preservation technique for the gentle treatment of food products. Information about the impact of HPP on lipophilic food ingredients (e.g., carotenoids, vitamin E) is still limited in more complex matrices such as kale. Both the variation of pressure levels (200–600 MPa) and different holding times (5–40 min) served as HPP parameters. Whereas a slightly decreasing solvent extractability mostly correlated with increasing pressure regimes; the extension of holding times resulted in elevated extract concentrations, particularly at high-pressures up to 600 MPa. Surprisingly, slightly increasing bioaccessibility correlated with both elevated pressures and extended holding times, indicating matrix-dependent processes during in vitro digestion, compared to results of extractability. Moreover, the verification of syringe filters for digest filtration resulted in the highest relative recoveries using cellulose acetate and polyvinylidene difluoride membranes. The α-tocopherol equivalent antioxidant capacity (αTEAC) and oxygen radical antioxidant capacity (ORAC) assays of treated kale samples, chopped larger in size, showed increased antioxidant capacities, regarding elevated pressures and extended holding times. Consequently, one may conclude that HPP was confirmed as a gentle treatment technique for lipophilic micronutrients in kale. Nevertheless, it was indicated that sample pre-treatments could affect HP-related processes in food matrices prior to and possibly after HPP.

High pressure processing and heat sterilization of kale: Impact on extractability, antioxidant capacity and storability of carotenoids and vitamin E

“…Reversed-phase HPLC coupled to diode array detection served for the analysis of xanthophylls, carotenes as well as chlorophyll a and chlorophyll b according to a previously published methodology [27].…”

“…Normal-phase HPLC coupled to fluorescence detection was modified from a previously published method using the same HPLC system and column [27]. Therefore, extract residues were subject to a solvent exchange and were redissolved in a mixture of n-hexane/ MtBE (93:7 = v/m), which was used for isocratic elution as well.…”

“…Sample extractions were performed according to a standardized method described by Schmidt et al [27]. Briefly, kale samples (0.5 g)…”

“…Especially, effects of HPP on lipophilic food ingredients (e.g., carotenoids, vitamin E) were less investigated while pressurerelated stabilities of hydrophilic vitamin C or B groups were reported more frequently in the past for varying matrices [22][23][24][25]. Since different food matrices were reported to have potential impacts on nutrient stability after treatments with high pressure [26], kale represents an interesting matrix that is less investigated and provides a relatively wide range of carotenoids and vitamin E as well as chlorophylls [27]. The impact of HPP and thermal sterilization on lipophilic ingredients in kale may be determined by applying a variety of techniques such as solvent extraction and high-performance liquid chromatography for investigating extractabilities of bioactive compounds.…”

“…The impact of HPP and thermal sterilization on lipophilic ingredients in kale may be determined by applying a variety of techniques such as solvent extraction and high-performance liquid chromatography for investigating extractabilities of bioactive compounds. Moreover, the use of lipophilic antioxidant capacity (L-AOC) assays such as (lipophilic oxygen radical antioxidant capacity (L-ORAC) and α-tocopherol equivalent antioxidant capacity (αTEAC) may be applied to provide still limited information about HPP effects on lipophilic ingredients in terms of a sum parameter including potentially more hydrophobic compounds than quantified via chromatographic methods [27][28][29][30].…”