Industrial freezing effects on the content and bioaccessibility of spinach (Spinacia oleracea L.) polyphenols

Abstract

BACKGROUNDSpinach is well recognized as a functional food owing to its diverse nutritional composition, including polyphenols. Freezing is an efficient preservation method that is used to maintain the physical and nutritional characteristics and extend the shelf life of spinach. The aim of this study was to determine the changes in polyphenols in the samples taken from various production steps of the industrial freezing process of spinach, and to evaluate the bioaccessibility of these bioactive compounds for raw material, by‐product, and frozen product using the standardized in vitro digestion model simulating the digestion in the mouth, stomach, and intestine.RESULTSUltra‐performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry and high‐performance liquid chromatography equipped with photodiode array detection analysis of spinach samples led to the identification of eight flavonoids and two phenolic acids. The changes occurring in flavonoids after blanching, chopping, and freezing steps were statistically not significant compared with the raw material (P > 0.05). On the other hand, by‐product was found to contain significantly lower amounts of flavonoids (98% in total) and phenolic acids (90% in total) (P < 0.05) compared with the raw material. Furthermore, after in vitro digestion, frozen spinach was found to contain higher amounts of bioaccessible flavonoids (15% in total) and phenolic acids (16% in total) compared with fresh spinach.CONCLUSIONOverall, the current study highlighted that industrial freezing might be a good strategy to preserve the polyphenol content of fresh spinach as well as to enhance the total amount of bioaccessible polyphenols.

Impact of Processing Approach and Storage Time on Bioactive and Biological Properties of Rocket, Spinach and Watercress Byproducts

“…The literature data agree with these results, although few studies were found under the same processing and freezing conditions in the literature for the studied byproducts. Kamiloglu [33] also studied TPC changes in spinach samples during industrial freezing, suggesting an excellent nutritional value during freezing storage and aligning with the present study data. As previously reported, after the increase in the TPC and antioxidant capacity stage, some losses were registered compared to the fresh forms with M6 in spinach, but a high nutritional value was registered.…”

“…However, in all cases, a significant improvement of these compounds was verified comparatively with fresh forms. Kamiloglu [33] studied the impact of industrial freezing on spinach polyphenols, suggesting that freezing can be an excellent strategy to preserve these bioactive groups and aligning with the present study results.…”

“…Other works focusing on fresh spinach's phenolic profile also suggested the hydroxycinnamic acid group as the most prevalent phenolic group in spinach [9,39,40]. In contrast, Kamiloglu [33] suggested flavonoids and phenolic acid (e.g., p-coumaric acid derivatives) as predominant polyphenols.…”

“…Other reason may be the interferent molecules existent in prepared extracts (e.g., proteins and sugars). These can react with Folin-Ciocalteu reagent, resulting in overestimation [33,41]. Table 4 lists all phenolic antioxidants identified and quantified in the rocket, spinach and watercress byproducts and their retention times and maximum absorption wavelengths (λ max).…”

Oil matrix modulates the bioaccessibility of polyphenols: a study of salad dressing formulation with industrial broccoli by‐products and lemon juice

“…Polyphenols from undigested samples were extracted as described previously 20 . Briefly, 2 mL of the sample was treated with 5 mL of 75% aqueous methanol containing 0.1% formic acid.…”