The pH is closely related to the growth of microorganism in
food. Below a pH of approximately 4.2, most microorganisms that
cause food poisoning are well controlled; however, lactic acid
bacteria and many species of yeasts and molds grow well at pH
levels below 4.2. In addition, bacterial spores are killed by heat
more rapidly at acidic pH values than at neutral pH (Rahman, 2007,
chap. 12). In the garlic sample heated at 85 C, the pH decreased to
below 4. Therefore, black garlic samples heated to 85 C may be
more biologically stable with respect to microbial growth. However,
this was not the case for the garlic sample heated at 40 C due
to its high pH.