Antimicrobial Agents Used in Starch-Based Packaging Material

Antimicrobial agents are the additives used for controlling the biological deterioration as well as to restrain the microbial growth, including pathogens. Many types of antimicrobial compounds, including natural extracts, chemical agents, enzymes, and probiotics, are potentially integrated into packaging materials. Majority of the antimicrobial compounds have been categorized as generally recognized as safe. Of late, the demand of consumers for the natural substances and chemical-free preservative food products is constantly increasing. The antimicrobial substances in large number may be integrated into the packaging materials to increase antimicrobial property to control the rate of grow'th of particular or a group of microbes in the headspace of a package, to ensure the safety of the food product, and to extend its shelf life. In culture media, strong antimicrobial activity against target microbes has been demonstrated by numerous antimicrobial agents. However, several antimicrobial agents used as food additives in packaging matrix have restricted effect on the microorganisms in foodstuff. The selection criteria of antimicrobial agents for food-packaging materials mainly depend on the characters of active agent and its mechanism of inhibition, organoleptic properties of active compounds, physico-chemical properties of food products, manufacturing process of packaging and its influence on the effectiveness of active agents, storage conditions, toxicity and regulatory issues, micro-flora of foods, physiology of target microbes, and release mechanism of the active substances into the foods (Coma, 2012). Thereafter, the classification of antimicrobial compounds can be done on the basis of their nature. Antimicrobial effects of various antimicrobial agents incoiporated in starch-based biopolymers are presented in Table 15.2.

Chemical Agents

Generally, organic acids are the major sources of chemical antimicrobial compounds used in food products, considering their effectiveness and low price. Their production is done through the process of chemical synthesis or alteration of natural acids (Han, 2005). These are potentially integrated into the packaging matrix because of their antimicrobial effect for a wide range of microbes. The growth of microbes is inhibited on the addition of organic acids through a decrease in pH, acidification of cytoplasm, affecting proton gradient cross the membrane, and a hindrance to the transport of chemicals through cell membrane (Naidu, 2000). Studies have shown the development and use of organic acid- contained biopolymer films having antimicrobial activity.

Salleh and Muhamad (20Ю) added lauric acid in wheat starch film and observed antimicrobial activity in the liquid culture and the solid media. Results indicated that film had more antimicrobial efficacy for Bacillus subtilis as compared to E. coli. Shen et al. (2010) reported that the incoiporation of potassium sorbate at the level of 15% (w/w) in sweet potato-starch film considerably reduced the count of E. coli on solid media as compared to control film.

Essential Oils

The aromatic and volatile oily extracts obtained from various plant parts are known as essential oils (Burt, 2004). However, due to a strong flavour, their direct inclusion into foods as preservatives is constantly limited. So, these oils may well be added to edible films or packaging films to evade the previously mentioned problem. In biobased films, normally used essential oils are cinnamon, clove, ginger, lemongrass, marjoram, thyme, oregano, sage, Ziziphora clinopodioides, and Eucalyptus globules. These proved quite effective against different microbes (Ahmad et al., 2012; Lee et al., 2015; Martucci et al., 2015; Hafsa et al., 2016; Ejaz et al., 2018). The antimicrobial activity of these essential oils may possibly be ascribed to their major phenolic or terpenic compounds, available in large quantity (up to 85%; Burt, 2004). Essential oils from different sources comprising different key compounds or a ratio of these compounds have diverse capacity to unite with membrane proteins of microbial cells as well as to alter membrane properties (Acevedo et al., 2015; Punia et al., 2019c). Pelissari et al. (2009) followed the agar disc diffusion method to explore the antimicrobial effect of oregano essential oil added into starch film and found significant inhibition in the growth of E. coli. B. cereus, and 5. enteritidis. Thyme essential oil incorporated in biodegradable nanocomposite film formed of sweet potato starch and montmorillonite nanoclay was reported to be effective against E. coli and 5. typhi (Issa et al., 2017).

TABLE 15.2

Antimicrobial Activity of Starch Based Antimicrobial Biopolymers

Coating Material

Antimicrobial Compounds

Microorganisms Used for Testing

Outcomes

References

Tapioca starch

Grape pomace extracts

Staphylococcus aureus and Listeria monocytogenes

Stronger inhibitory effect on S. aureus compared to L monocytogenes

Xu et al.. 2018

Corn starch-beeswax

Laurie arginate + natamycin

Rhizopus stolonifer, Colletrotrichum gloeosporioides, Botrytis cinerea, and Salmonella Saintpau

Completely inhibited all the tested microorganisms

Ochoa et al.. 2017

Starch film

Chitosan

S. enteritidis

Inhibited tested microorganism

Durango et al., 2006

Starch film

Laurie acid

Bacillus subtilis and E. coli

Inhibited both the tested microorganisms

Salleh et al.. 2007

Starch film

Lysozyme

B. thermosphacta B2

Inhibited tested microorganism

Nam et al.. 2007

Starch film

Potassium sorbate

E. coli and S. aureus

Inhibited E. coli but not S. aureus

Shen et al.. 2010

Starch film

Potassium sorbate

S. typliimurium and E. coli

Inhibited S. typhimurium and E. coli 0157:H7 by 4 and 2 logs, respectively

Baron and Sumner, 1993

Starch-alginate

Lemongrass oil

E. coli 0157:H7

Inhibited tested microorganism

Maizura et al.. 2008

Starch-chitosan

Oregano Essential oils

E. coli 0157:H7, S. aureus, S. enteriditis, and />’. cereus

Inhibited all the tested microorganisms

Pelissari et al., 2009

Starch

Grape seed extract

L. monocytogenes, E. coli, E. faecalis, E. faecium,

S. typliimurium, and />’. thermosphacta B2

Reduced 1.3 log CFU mL-1 of B. thermosphacta B2 on pork loin; inhibited gram-positive bacteria on solid media but not gram-negative bacteria

Corrales et al.. 2009

Starch

Pomegranate peel powder

S. aureus and Salmonella

Reduced the count of bacteria tested

Amjad et al.. 2018

 
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