EVALUATION OF OXYGEN ABSORBER ON ANTIMICROBIAL PRESERVATION OF LASAGNA-TYPE FRESH PASTA UNDER VACUUM PACKED

O 2 absorbent system was evaluated on the inhibition of microorganisms growth in fresh lasagna pasta during storage at 10±2oC. Fresh lasagna pasta was produced with and without potassium sorbate and acondicionated in high O 2 barrier bags containing a O 2 absorber sachet in the head-space. Three treatments were obtained: pasta with potassium sorbate, pasta without potassium sorbate packed with sachet and pasta without potassium sorbate packed without sachet. In all treatments, the pasta were vacuum packed, randomly distributed at temperature of 10±2oC and microbiologically evaluated for molds and yeast, Staphylococcus spp, total coliforms and Escherichia coli countings. All the treatments were effective in inhibiting the growth of the microorganisms evaluated during 30 storage days. The treatment using O 2 -absorber in the pasta without preservative, inhibition of 1 and 1.5 logarithmic cycles was observed for the molds and yeasts and Staphylococcus spp, respectively. No differences were observed among treatments for coliforms countings.


INTRODUCTION
Maintaining the quality of a food product and, consequently, its preservation, is based principally on the inhibition or prevention of microbial growth (ALLARCON & HOTCHKISS, 1993).Food can still be preserved by the addition of antimicrobial substances that prevent or inhibit the development of microorganisms.However consumers are currently demanding products that have better ''in natura'' qualities.
Microbiota growth is determined by the presence of oxygen, favoring the growth of aerobic organisms and, consequently, the lack of oxygent will allow facultative anaerobes to become dominant.
The presence of oxygen inside the packages is due to flaws in the packaging process, such as mixture of gases containing oxygen residues, inefficient vacuum, as well as high permeability -oxygen rates of the package utilized.Thus, packaging research and developments have been carried out aiming at elimination of residual oxygen.
Within this context, the concept of active packaging has been introduced.This technology involves an interaction of the package with the product, modifying its properties as desired.This new concept of packaging includes the O 2 absorbers (BERENZON & SAGUY, 1998;HAN, 2002;VERMEIREN et al., 1999), also called deoxidizers or oxygen scavengers.
According to Abbott (2002), one of the main advantages of using absorbers is their capacity to reduce the O 2 levels to less than 0.01%, which is lower than those typically found (0.3-3%) using traditionally modified atmosphere packaging (MAP) vacuum packaging or substitution of the internal atmosphere by inert gas.Thus, this method has attracted interest as a novel packaging technology applied to reduce the oxygen level inside the packages to preserve food quality (ABE & KONDOH, 1989;NAKAMURA & HOSHINO, 1983).The method prevents the growth of aerobic microorganisms, delays oxidation of lipids and flavor compounds and may still replace chemical pesticides to prevent damage caused by larvae and insects.Some of its disadvantages are the possibility of packaging collapse which can be avoided by using an O 2 absorber and CO 2 generator system.In the case of absorbers in sachet form, one can also cite the need of free airflow around the sachet to enhance the O 2 scavenging capacity inside the package (AZEREDO et al., 2000;SMITH et al., 1990SMITH et al., , 1995)).
In bakery products, molds are the major deteriorating agents.Besides the visual repulsion caused by their growth, these microorganisms are responsible for an undesirable flavor and production of mycotoxin and allergic compounds.
Some data have shown an extension of the shelflife of these products with the use of O 2 absorbers, especially iron powder based O 2 absorbent sachets (NAKAMURA & HOSHINO, 1983).A research work showed that the use of these sachets was a more efficient alternative than that of nitrogen atmosphere in the control of Aspergillus niger and Penicillium spp, common contaminants of bakery products (SMITH et al., 1986).The study revealed that in products packed with air, nitrogen and CO 2 /N 2 (60:40), a visible growth of fungi occurred after 9, 11 and 16 days, respectively.When using the same atmospheres modified associated with O 2 -absorber sachet, mold growth was not visible up to 60 storage days at 25C.The package utilized was nylon and polyethylene laminate with mean permeability of 40 cm 3 .m - day -1 for O 2 , 14 cm 3 .m- 2 day -1 for N 2 and 155 cm 3 .m - day -1 for CO 2 , at 25C and 100% relative humidity.
The objective of this work was to evaluate the efficiency of a commercial oxygen absorber system in inhibiting the growth of molds and yeasts, Staphylococcus spp, total coliforms and Escherichia coli countings in lasagna, type fresh pasta.

MATERIAL AND METHODS
An iron based O 2 absorbent system in sachet form, was utilized.The model was the FT-300, meant to be used in products with maximum water activity (aw) of 0.85, with capacity to absorb up to 300 mL of oxygen, according to the manufacturer.The basic ingredients used in the pasta production were: wheat flour, oil, salt and water and potassium sorbate as chemical preservative.
The fresh pasta was produced in a local industry and two bulks were prepared: with and without potassium sorbate.The pasta was vacuum packed in a commercially used, multi-layered package made of polivinylidene (PVdC) and poliethylene (PE), 80 µm thick, 53 g/m 2 and 8.63 cm 3 / m 2 .day.atm of permeability to O 2 .Package permeability was determined in the equipment Oxtran 2/20 (MOCON) at 23 o C. All the pasta was vacuum packed.The bags containing the pasta without sorbate an O 2 -absorber sachet was added in the head space of the package.The treatments were randomly divided and stored at a cooling temperature (10±2 o C).
Pasta samples of the different treatments were submitted to molds and yeast (FCU/g), total coliforms and E. coli (NMP/g) and Staphylococcus spp (FCU/g) countings, according to APHA (VANDERZANT & SPLITTSTOESSER, 1992).Water activity in the fresh pasta was performed using the equipment Aqualab, at 25 o C. The averages of the microbiological counts were compared by Tukey test.

RESULTS AND DISCUSSION
All the treatments were efficient in inhibiting the growth of molds and yeasts, at 10±2 o C, for 45 days, since the maximum count of 10 4 FCU/g established by the Brazilian legislation was not reached (Figure 1).However, until the 30th day, the absorber treatment was the most efficient (p<0.05) with a count around 10 2 FCU/g of molds and yeasts.
The molds commonly found in fresh lasagna pasta are strictly aerobic and should not grow in the products when vacuum-packed.However, as pointed out by Hotchkiss (1988), Rooney (1995) andVermeiren et al. (1999), this technique does not eliminate all the oxygen from the package and does not control the oxygen permeated through it.Therefore, the existence of residual oxygen Evaluation of oxygen absorber on antimicrobial preservation... Ciênc. agrotec., Lavras, v. 30, n. 6, p. 1135-1138, nov./dez., 2006 occurs under vacuum packaging conditions, allowing the growth of these microorganisms.
FIGURE 1 -Decimal logarithm of the number of molds and yeasts (FCU/g) in lasagna type fresh pasta ( Absorber; Vacuum; Chemical preservative).Averages followed by the same letters do not differ by Tukey test (p < 0.05).
According to Cruz (2003) the oxygen rate of the O 2absorber sachet is 312.50 cm 3 /day, higher than the oxygen permeability rate of the bag (0.518cm 3 /day).Therefore, the sachet contributed to maintain a low oxygen concentration inside the bags containing the sachet, what explain the lower molds and yeasts countings until the 30 th day of storage.
The treatment using chemical preservative shown to be efficient in inhibiting the growth of molds and yeasts for 45 days.The chemical preservative, sorbic acid, not only inhibits growth but also eliminates vegetative cells.This preservative is added as salts, such as potassium sorbate, which, when in contact with water, return to its acid form, penetrating in the microorganism cell in non-dissociated form.The dissociation of the acid occurs in the microbial cytoplasm, leading to a lowering of the intracellular pH, causing the destruction of the microorganism.Thus, the preservative decreases the number of viable cells, thereby extending the shelf life of the product.
Staphylococcus spp are facultative anaerobic microorganisms, which grow between -150 and + 50 mV.Hence, restricting the oxygen, e.g., with vacuum application only, would not be sufficient to inhibit it.It was observed in this experiment that the use of vacuum in conjunction with O 2 absorber was the most efficient treatment (p<0.05) to inhibit the growth of this microorganism up to 30 days, when the Staphylococcus.spp count was around 1.5 logarithmic cycles smaller (Figure 2) than the other treatments.It should be mentioned that the initial counting FIGURE 2 -Decimal logarithm of the number of Staphylococcus spp (FCU/g) of lasagna type fresh pasta ( Absorber; Vacuum; Chemical preservative).Averages followed by the same letters do not differ statistically by the Tukey test (p < 0.05).
of Staphylococcus spp was 1x10 2 FCU/g and the Brazilian regulation specify the maximum counting of 5x10 3 FCU/g for this microorganism (ANVISA, 2000).
The growth of total coliforms did not present significant difference (p<0.05),among the treatments until the 30 th day of storage.
Even though vacuum packed lasagna pasta presented the lower coliforms counting (p<0.05) after 45 days (Figure 3), the treatments did not reach the count of 10 2 NMP/g, established by the Brazilian legislation.It should also be mentioned that for all the treatments E. coli count was lower than 3 NMP/g, over the 45 storage days.

FIGURE 3 -
FIGURE 3 -Decimal logarithm of the number of of total coliforms (NMP/g) of lasagna type fresh pasta ( Absorber; Vacuum; Chemical preservative).Averages followed by the same letters do not differ statistically by the Tukey test (p < 0.05).