IJUP08 - Universidade do Porto

In vitro assessment of whey edible coats with antimicrobial
features against differents microbial strains
A. Santos, M. Leão, O. Ramos, M. Pintado, and X. Malcata
Escola Superior de Biotecnologia - Universidade Católica Portuguesa
Rua Dr. António Bernardino de Almeida, P-4200-072 Porto, Portugal
A new generation of food packages is on the way – as traditional concepts were hampered
in their ability to further extend shelf-life of food products, coupled to considerably high
ecological footprints. One element of such a generation takes advantage of coats that
inhibit undesirable microbial growth; however, most commercial solutions already made
available in the market include compounds – which cannot be ingested. Edible coatings
based on milk proteins – viz. whey proteins, have meanwhile been developed for use as
protective layers in a variety of foods. Unfortunately, their main functionality relates to
barrier properties, so there is large room for improvement in appearance. Development of
edible coats exhibiting general antimicrobial properties is thus an issue of practical
relevance; however, a general solution may not exist, as different spoilage/pathogenic
microflora have been associated to the food surface. Consequently, the objective of this
research effort was to assess – via in vitro tests, the efficacy of several formulated
antimicrobial edible coats, based on whey protein isolates as base coating material, and
glycerol as plasticizer. The antimicrobial activity of several antimicrobial agents — e.g. a
polysaccharide (oligochitosan), organic acid (lactic acid) and a bacteriocin (nisin) were
tested against yeasts (e.g. Yarrowia lipolytica) and bacteria (Escherichia coli and Listeria
innocua) at an inoculum level of 10 5 cfu/ml. The inhibitory effect of said antimicrobials
was initially tested in culture media and in edible coats, which remained in contact with
said microbial strains for 24 h. Afterwards, the best antimicrobial systems were selected.
Lactic acid (at 0.6%) and oligochitosan (at 2%) yielded the strongest effect under the
conditions tested against previously strains. Different coatings showed different
antimicrobial behaviors – depending on the microbial agent in stake; however, association
of antimicrobial agents increased (as expected) the individual antimicrobial activities.
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