Novel, Edible Melanin-Protein-Based Bioactive Films for Cheeses: Antimicrobial, Mechanical and Chemical Characteristics

Abstract

The cheese rind is the natural food packaging of cheese and is subject to a wide range of external factors that compromise the appearance of the cheese, including color defects caused by spoilage microorganisms. First, eight films based on whey protein isolate (WPI) coatings were studied, of which IS3CA (WPI 5% + sorbitol 3% + citric acid 3%) was selected for presenting better properties. From the IS3CA film, novel films containing melanin M1 (74 µg/mL) and M2 (500 µg/mL) were developed and applied to cheese under proof-of-concept and industrial conditions. After 40 days of maturation, M2 presented the lowest microorganism count for all the microbial parameters analyzed. The cheese with M2 showed the lowest lightness, which indicates that it is the darkest cheese due to the melanin concentration. It was found that the mechanical and colorimetric properties are the ones that contribute the most to the distinction of the M2 film in cheese from the others. Using FTIR-ATR, it was possible to distinguish the rinds of M2 cheeses because they contained the highest concentrations of melanin. Thus, this study shows that the film with M2 showed the best mechanical, chemical and antimicrobial properties for application in cheese.

Keywords: bioactive coatings; cheese; edible packing; melanin; whey protein isolate.

Figure 1

Assay design of application of melanin WPI coatings in cheese under industrial conditions.

Figure 2

Mechanical properties of WPI-based films: IG3CA—WPI 5% + glycerol 3% + citric acid 3%; IG3LA—WPI 5% + glycerol 3% + lactic acid 3%; IS3CA—WPI 5% + sorbitol 3% + citric acid 3%; IS3LA—WPI 5% + sorbitol 3% + lactic acid 3%; IG5CA—WPI 5% + glycerol 5% + citric acid; IG5LA—WPI 5% + glycerol 5% + lactic acid; IS5CA—WPI 5% + sorbitol 5% + citric acid 3%; IS5LA—WPI 5% + sorbitol 5% + lactic acid 3%. Different lowercase letters (a–e) represent significant differences (p ≤ 0.05).

Figure 3

Mechanical properties of films for coated cheese: CF—commercial film (RIOCOBERT and VIPLAST-1AX); M1—WPI 5% + sorbitol 3% + citric acid 3% + natamycin (3.5 mg/mL) + nisin (50 IU/mL) + melanin (74 µg/mL); M2—WPI 5% + sorbitol 3% + citric acid 3% + natamycin (3.5 mg/mL) + nisin (50 IU/mL) + melanin (500 µg/mL). Different lowercase letters (a–b) represent significant differences (p ≤ 0.05).

Figure 4

Color parameters and total color differences of WPI films from film-forming solutions subjected to different formulations: IG3CA—WPI 5% + glycerol 3% + citric acid 3%; IG3LA—WPI 5% + glycerol 3% + lactic acid 3%; IS3CA—WPI 5% + sorbitol 3% + citric acid 3%; IS3LA—WPI 5% + sorbitol 3% + lactic acid 3%. Different lowercase letters (a,b,c) represent significant differences (p ≤ 0.05).

Figure 5

Proof-of-concept cheese evolution with different coatings during 40 days of ripening. The little flags sticking out of the cheese rinds indicate the type of coating tested.

Figure 6

Microbial analysis of cheese rinds with coatings. T0—cheese without coating at 0 days of maturation. C-40—cheese control after 40 days of maturation (cheese without coating). CF-40—cheese with commercial formulation coating after 40 days of maturation. M1-40—cheese with melanin film 1 after 40 days of maturation. M2-40—cheese with melanin film 2 after 40 days of maturation.

Figure 7

Color parameters and total color difference of cheese rinds with films after 40 days of maturation under industrial conditions. C: cheese control after 40 days of maturation (cheese without coating). CF: cheese with commercial formulation coating after 40 days of maturation. M1: cheese with melanin WPI film 1 after 40 days of maturation. M2: cheese with melanin WPI film 2 after 40 days of maturation. Different lowercase letters (a–d) represent significant differences (p ≤ 0.05).

Figure 8

Score plot of the principal components of the PCA (mean-centered) performed with ten variables; (a) PC1 vs. PC2 and (b) PC1 vs. PC3. C: cheese rind control after 40 days of maturation (cheese without coating). CF: cheese rind with commercial formulation coating after 40 days of maturation. M1: cheese rind with melanin WPI film 1 after 40 days of maturation. M2: cheese rind with melanin WPI film 2 after 40 days of maturation. Microbial parameters: microorganisms at 30 °C (M30), Pseudomonas spp. (Pseud), yeasts and molds. Mechanical properties: tensile strength (TS), thickness (T) and extensibility (E%). CIEL*a*b* spaces: lightness (L), red–green (a*) axis and yellow–blue (b*) axis.

Figure 9

FTIR-ATR spectrum for cheese samples. M1: cheese with melanin WPI film 1 after 40 days of maturation. M2: cheese with melanin WPI film 2 after 40 days of maturation. CF: cheese with commercial formulation coating after 40 days of maturation. C: cheese control after 40 days of maturation (cheese without coating).

Figure 10

(a) Score plot of the first two principal components of the PCA (mean-centered) performed with FTIR-ATR spectra, and (b) loading representation of cheese rinds using the first-derivative Savitzky–Golay spectra transform with 17 smoothing points. C: cheese rind control after 40 days of maturation (cheese without coating). CF: cheese rind with commercial formulation coating after 40 days of maturation. M1: cheese rind with melanin WPI film 1 after 40 days of maturation. M2: cheese rind with melanin WPI film 2 after 40 days of maturation.