Survival of Listeria innocua in Rainbow Trout Protein Recovered by Isoelectric Solubilization and Precipitation with Acetic and Citric Acids†

Abstract

During mechanical fish processing, a substantial amount of protein is discarded as by-products. Isoelectric solubilization and precipitation (ISP) is a process that uses extreme pH shifts to solubilize and precipitate protein from by-products to recover previously discarded protein. Typically, strong acids are used for pH reduction, but these acids do not have a pasteurization effect (6 log reduction) on bacterial load; therefore, organic acids were used during ISP processing to test the impact on Listeria innocua concentrations. Headed and gutted rainbow trout (Oncorhynchus mykiss) were inoculated with L. innocua, homogenized, and brought to the target pH with granular citric acid (pH 2.0 and 2.5) or glacial acetic acid (pH 3.0 and 3.5). Proteins were solubilized for 10 min at 4°C, and insoluble components (e.g., skin and insoluble protein) were removed by centrifugation. The remaining solution was pH shifted to the protein isoelectric point (pH 5.5) with sodium hydroxide, and precipitated protein was separated from the water. Microbial cells for each component (proteins, insolubles, and water) were enumerated on modified Oxford agar (MOX) and tryptic soy agar with 6% yeast extract (TSAYE). The sums of the surviving cells from each component were compared with the initial inoculum levels. No significant differences were observed between results obtained from TSAYE and from MOX (P > 0.05). Significant reductions in microbial populations were detected, regardless of pH or acid type (P < 0.05). The greatest reduction was at pH 3.0 with glacial acetic acid, resulting in a mean reduction of 6.41 log CFU/g in the recovered protein and 5.88 log CFU/g in the combined components. These results demonstrate the antimicrobial potential of organic acids in ISP processing.

Impact of sarcoplasmic proteins on texture and color of silver carp and Alaska Pollock protein gels

“…The traditional acid used in ISP is hydrochloric acid (HCl); however, researchers have demonstrated that using organic acids may have bactericidal effects Otto, Paker, et al, 2011). The traditional processing base used in ISP is sodium hydroxide (NaOH) which increases the sodium content of the recovered protein fraction (Paker, Beamer, Jaczynski, & Matak, 2013a).…”

The Effect of Using Citric or Acetic Acid on Survival of Listeria monocytogenes during Fish Protein Recovery by Isoelectric Solubilization and Precipitation Process

“…Lansdowne and others (2009) demonstrated that pH shifts with HCl used in ISP resulted in significant reductions in L. innocua populations, but did not demonstrate a net pasteurization effect, described as a 6‐log reduction in Listeria numbers (USDA 2001). Otto and others (2011) verified a net pasteurization effect on L. innocua during ISP using organic acids. Therefore, the objectives of this study were: (1) to determine the response of L. monocytogenes to ISP processing of rainbow trout ( Oncorhynchus mykiss ) with citric and acetic acids; (2) to compare the survival rates with L. innocua ; and (3) to determine if L. innocua is an appropriate surrogate for L. monocytogenes in future ISP processing studies.…”

“…Methodology for the ISP process has been described elsewhere (Lansdowne and others 2009; Otto and others 2011). Briefly, inoculated fish paste (107 g) was homogenized with 693 mL distilled, deionized water in an autoclaved 2000 mL glass beaker (Figure 1).…”

“…Recently, L. innocua has been used as a surrogate for L. monocytogenes in studies examining different antimicrobial effects of processing treatments. Chill brine and lactic acid bacteria treatments (Boyer and others 2009), temperature treatments (Nufer and others 2007), liquid smoke treatments (Milly and others 2008), high pressure homogenization and nisin treatments (Pathanibul and others 2009), and organic and inorganic acid treatments (Lansdowne and others 2009; Otto and others 2011) have all utilized L. innocua as a surrogate. However, there is no data available that directly compare L. monocytogenes and L. innocua survival rates during processing that utilizes extreme pH shifts.…”

Dynamic rheology and endothermic transitions of proteins recovered from chicken-meat processing by-products using isoelectric solubilization/precipitation and addition of TiO2

“…ISP allows high protein recovery yields while significantly reducing fat content (Chen & Jaczynski, 2007b;). Due to extreme pH shifts, ISP results in mild, non-thermal pasteurization (Lansdowne, Beamer, Jaczynski, & Matak, 2009a, 2009bOtto et al, 2011). Therefore, ISP offers several advantages over mechanical deboning and may be a useful and novel technology to recover functional proteins from low-value dark chicken-meat processing by-products for subsequent inclusion in value-added meat products.…”