Impact of the frozen vegetable processing chain on health-related compounds: A pilot-scale case study on leek (Allium ampeloprasum var. porrum)

Abstract: The impact of pretreatment (i.e., unblanched vs. flash-blanched for 90 s at 70°C), freezing rate (i.e., −0.01, −6.25, −7.5, or −10°C/min), storage (i.e., 16 weeks at −15°C), and thawing (i.e., via microwaves, at 20°C, 7°C, or 4°C) on vitamin C and S-alk(en)yl-L-cysteine sulfoxides (ACSOs) stability was evaluated in diced leeks on pilot-scale. In unblanched, diced leeks, >70% of vitamin C was lost during frozen storage and enzymatic conversions of vitamin C and ACSOs could occur further during thawing, independent from thawing method. In this context, flash-blanching showed potential to ensure compound stability through frozen storage and thawing, without indicating major tissue damage (i.e., drip loss). Although flash-blanching reduced the initial vitamin C concentration by 36%–39%, these samples showed 39%–60% higher vitamin C concentrations at the end of storage. ACSOs stability through frozen storage seemed not to be impacted by flash-blanching. Large variability in ACSOs concentrations between samples was observed. This was attributed to deviations in the industrial-relevant cut of 40% white and 60% green, which could have overshadowed certain effects. Furthermore, the freezing rate did not affect the stability of vitamin C and ACSOs during frozen storage of flash-blanched diced leeks. Additionally, no differences in drip loss of flash-blanched diced leeks frozen at different rates were observed. Quick-freezing to a higher end temperature could open perspectives for reducing energy up to 26% (theoretical simulation). However, this should be balanced with product temperature increase after individual quick freezing (IQF) and before bulk storage. Practical Application: Variations in the characteristics of fresh leeks, particularly the green-to-white ratio, not only influence the initial concentrations of health-related compounds but also affect concentrations throughout processing. Flash-blanching showed potential to maintain concentrations of vitamin C and S-alk(en)yl-L-cysteine sulfoxides (ACSOs) through frozen storage and thawing, without indicating major tissue damage. Applying lower freezing rates could open perspectives for reduced freezing costs, without sacrificing quality.