Comparison of the influence of citric acid and acetic acid as simulant for acidic food on the release of alloy constituents from stainless steel AISI 201

Abstract

a b s t r a c tTo ensure the safety of metals and alloys intended for food contact, a new European test protocol (CoE protocol) using citric acid as a food simulant was published in 2013. This study investigated the influence of citric acid and exposure conditions on the metal release from an austenitic manganese stainless steel (AISI 201). Exposures in 5 g/L citric acid resulted in significantly lower metal releases compared with specific release limits set by the CoE protocol. 5 g/L (0.3 vol%) citric acid was more aggressive than 3 vol% acetic acid (Italian protocol) due to higher metal complexation. Studies on abraded surfaces revealed that most metals were released during the first 0.5 h of exposure due to surface passivation. Surface abrasion, increased temperature (40-100°C), increased surface area to solution volume ratio (0.25-2 cm 2 /mL) and increased citric acid concentration (0-21 g/L) all resulted in increased released metal quantities.

Metal Release Mechanisms for Passive Stainless Steel in Citric Acid at Weakly Acidic pH

“…11 Cr release was however more dependent on the citric acid concentration and did increase up to 5 g/L citric acid. 11 5 g/L citric acid is the suggested citric acid concentration in the food simulant in the recently new European testing guideline for metals and alloys, and is based on common citric acid concentrations in food.…”

“…11 Cr release was however more dependent on the citric acid concentration and did increase up to 5 g/L citric acid. 11 5 g/L citric acid is the suggested citric acid concentration in the food simulant in the recently new European testing guideline for metals and alloys, and is based on common citric acid concentrations in food. 1 Based on literature data, 11 we expect deviations from the citric acid concentration of this study to be of minor importance for the metal release mechanism at pH 4.8 and 6.4, if the citric acid concentration is not below 0.1 g/L.…”

“…10,11,27 It seems that direct surface oxide dissolution processes (see Eqs. 2-4 and introduction) play an important role, both for the initial metal release and as contribution to surface passivation.…”

“…11 5 g/L citric acid is the suggested citric acid concentration in the food simulant in the recently new European testing guideline for metals and alloys, and is based on common citric acid concentrations in food. 1 Based on literature data, 11 we expect deviations from the citric acid concentration of this study to be of minor importance for the metal release mechanism at pH 4.8 and 6.4, if the citric acid concentration is not below 0.1 g/L. Figure 7 summarizes proposed metal release mechanisms from stainless steel (grade 304) in citric acid (5 g/L) at 40…”

Overview of citric acid production from Aspergillus niger

“…The drawback of using yeast is that it produces large quantities of isocitric acid, which is an undesirable by-product; therefore, mutant strains that have low aconitase activity are required. In addition, the increasing cost of oil makes it less feasible economically as oils are now used as the principal carbon source, in a manner analogous to the previous use of alkanes (Mazinanian et al 2015).…”