Sensory changes and microbial development on minimally processed lettuce

© 2018 International Society for Horticultural Science. All rights reserved. Lettuce heads (Lactuca sativa L. `Romaine¿) were minimally processed as in commercial practice. Outer leaves and stem were removed and lettuce leaves were cut at 10°C into about 2-3 cm wide and 10-12 cm2. Lettuce pieces were washed-disinfected at 10°C either with tap water or with water containing 120 ppm chlorine and 200 ppm citric acid (pH=6.8). After centrifugation pieces were packed in 250 g bags of 35 µm thickness microperforated oriented polypropylene (MOPP) or standard OPP (SOPP) films, in passive or active (4% O2 and 96% N2) modified atmosphere packaging (MAP). The bags were then stored for 8 days at 1 or 5°C. Sensory changes and microbial growth were monitored. Independently of temperature at the steady state in passive MAP with MOPP bags an atmosphere of 18.3% O2, 0.8% CO2 and 0.1 ppm C2H4 was reached while with SOPP film it was 10.1% O2, 6.7% CO2 and 1.8 ppm C2H4. However, in active MAP within MOPP bags an atmosphere of 17.9% O2, 1.3% CO2 and 0.1 ppm C2H4 was achieved while with SOPP it was 3.2% O2, 6.2% CO2 and 2.2 ppm C2H4. After 8 days of storage, no influence of washing solution neither of MAP method on overall visual quality (OVQ) of lettuce pieces was found. However, as expected, when storage temperature increased, OVQ decreased. At the end of storage a relatively good microbial quality for human consumption was reached with moderate (7.53 log CFU g-1) aerobic counts, according to normative for microbial safety.