Control of Alicyclobacillus acidoterrestris in apple juice by citrus extracts and a mild heat-treatment

This paper reports on the use of different citrus extracts (biocitro, lemon extract and neroli) for the inhibition of the spores of two strains of Alicyclobacillus acidoterrestris; the research included 3 steps. First, the bioactivity of citrus extracts was assessed under in vitro conditions using a modified micro-dilution method; the concentration of extracts was from 20 to 500 ppm. Then, biocitro and lemon extract (0–80 ppm) were combined with two different thermal treatments (at 70 and 80 °C for 3–6 min) through a fractional factorial design and finally a treatment at 80 °C for 6 min was combined with either biocitro (80 ppm) or lemon extract (80 ppm) and tested in apple juice. Biocitro and lemon extract showed MIC values (Minimal Inhibitory Concentration) from 160 to 500 ppm; their effect could be enhanced by a thermal treatment at 80 °C for 3–6 min, both under in vitro conditions and in apple juice. Finally, biocitro or lemon extract could be added before and after the thermal treatment without any significant loss of their bioactivity.