Two potato cultivars, Burbank and Norkotah, were washed, sanitized, peeled, sliced and dipped into antibrowning solutions of 3% sodium acid sulfate (SAS), citric acid (CA), sodium erythorbate (SE), malic acid (MA), sodium acid pyrophosphate (SAPP), or a combination of SAS, CA, and SE. Kinetics of polyphenol oxidase (PPO) obtained from crude potato extract exposed to antibrowning solutions at various concentrations and pHs were measured by UV-VIS spectroscopy. The color of slices dipped in antibrowning solutions at pHs 2 to 7 and stored at 4 C for 15d were measured every 5 d by colorimeter. Headspace analysis of volatile in raw and cooked potato samples was performed by a Selected Ion Flow Tube Mass Spectrometer (SIFT-MS) and SIMCA analysis of concentrations and their calculated relative aroma values (RAV) determined interclass distance and separation. Microbial growth was measured at 15 d. At unadjusted pHs, the PPO kinetics of the control and SAPP was not significantly different, SAS, CA and MA had some inhibition and SE and SAS-CA-SE stopped the reaction. At pH 5 to 7, only SE and SAS-CA-SE were effective PPO inhibitors. Based on the color of potato slices, SE was the most effective antibrowning agent at pH 2 to 7, but SAS was most effective at unadjusted pHs. Volatiles at high concentrations in raw potato were ethanol, hexanal, isobutane, methanol, pentanal, and propanal in both Burbank and Norkotah varieties. After potatoes were cooked, the same volatile compounds were present but in higher amounts. Several more volatiles significantly increased in cooked samples including 2,3-butanedione, 2-methylbutanal, 2-methylpropanal, benzaldehyde, methanol, and methional.
SIMCA analysis showed that the cooking process made volatile profiles more similar to each other and the control. When analyzing RAV values by SIMCA, 2-isopropyl-3-methoxypyrazine and dimethyl trisulfide, having the highest RAV values and highest discriminating powers, contribute to raw potato odor the most and most likely to show noticeable difference between treatments. Differences between cooked samples would not be noticeable by the consumer because volatiles with high discriminating powers (DP) have low RAVs. SAS, CA, and SAS-CA-SE treatments inhibited bacterial, yeast and mold counts but SAPP, control, and SE did not, most likely due to pH.
Practical Application
Antibrowning agents improve the inhibition of polyphenol oxidase which is responsible for enzymatic browning, increasing shelf life and consumer acceptability of processed raw potato products by preserving the color. Their effectiveness was shown to be due to a pH effect, except SE, which was not pH dependent. MA, CA, and SAS-CA-SE, proved themselves to be better acidulants, and were more favorable than the currently used SAPP for inhibition of color change as well as growth of spoilage bacteria, yeast, and mold.