ESTIMATION OF SHELF-LIFE OF HOT DOG SAUSAGE

Abstract

This study aimed to determine shelf-life of vacuum packed hot dog sausages stored at 2°, 6.5°, 15° and 21°C. Besides, it also aimed to identify the main causes of spoilage and to apply survival analysis for evaluating the results. End of shelf-life was determined when lactic bacteria counts reached 10^sup 7^ cfu/g with viscosity formation, harming the appearance of sausages. Contamination by such bacteria occurred due to manipulation after thermal treatment during packing process and, also, due to thermo tolerance of these microorganisms. Samples were, then, exposed to different temperatures and monitored at different periods. Packs considered unsuitable for consumption according to microbiological evaluation, combined with sensorial evaluation were considered as "fail" and suitable packs were considered "censored". With survival analysis it was possible to establish a shelf-life of 43 days for sausages kept at 2°C, 21 days for sausages kept at 6.5°C, 5 days for sausage kept at 15°C and 2.6 days for sausage kept at 21°C. So, it can be concluded that lactic bacteria are the main cause of sausage deterioration and that survival analysis can be used for shelf-life determination of food products. [PUBLICATION ABSTRACT]

Headnote

ABSTRACT

This study aimed to determine shelf-life of vacuum packed hot dog sausages stored at 2°, 6.5°, 15° and 21°C. Besides, it also aimed to identify the main causes of spoilage and to apply survival analysis for evaluating the results. End of shelf-life was determined when lactic bacteria counts reached 10^sup 7^ cfu/g with viscosity formation, harming the appearance of sausages. Contamination by such bacteria occurred due to manipulation after thermal treatment during packing process and, also, due to thermo tolerance of these microorganisms. Samples were, then, exposed to different temperatures and monitored at different periods. Packs considered unsuitable for consumption according to microbiological evaluation, combined with sensorial evaluation were considered as "fail" and suitable packs were considered "censored". With survival analysis it was possible to establish a shelf-life of 43 days for sausages kept at 2°C, 21 days for sausages kept at 6.5°C, 5 days for sausage kept at 15°C and 2.6 days for sausage kept at 21°C. So, it can be concluded that lactic bacteria are the main cause of sausage deterioration and that survival analysis can be used for shelf-life determination of food products.

Key words: lactic bacteria, shelf-life, survival analysis.

INTRODUCTION

Industrialized products are more and more practical, ready to eat, being the only work to open the pack. Besides practicality, industrialized food products also present a larger shelf-life than raw and not processed food products, making storage easier.

Shelf-life is an important attribute of food products. It can be defined as the time since production and packing until it is no more viable for human consuming. So, shelf-life is related to total quality of food products and directly linked to production, projection, ingredients characteristics, handling process and storage. Besides, shelf-life depends on type of food, being essential that manufacturers identify intrinsic and extrinsic parameters that influence this period.

Prediction of shelf-life is not an easy task, being the result not always accurate. However, it is very important to obtain maximum information about food product under analysis once it will allow a more precise shelf-life estimation and guiding regarding to the more adequate conditions for conserving such food product.

Microbiological analysis of total plate count and lactic bacteria count, physicochemical analysis of pH and sensorial analysis were performed in order to evaluate the spoilage process that occurs during storage. The present work aimed to estimate shelf-life of vacuum packed hot dog sausages stored at 2°, 6.5°, 15° and 21°C using survival analysis.

MATERIALS AND METHODS

Sampling

The present study was performed with 135 samples of sausage collected immediately after packing. Each sample represents 1 (one) vacuum-packed pack containing 1 kg of product. The packs were used for shelf-life, being stored in refrigerator with controlled temperature at 2°, 6.5°, 15°, and 21°C. Visual inspections were periodically performed in order to detect viscosity inside the packs. Microbiological, physicochemical and sensorial analyses were carried out according to the pre-determined time intervals.

Samples presenting excessive viscosity or microbiological countings higher than 10^sup 7^ cfu/g were considered unsuitable for consumption. These samples were labeled as "fail". Samples considered suitable for consumption were labeled as "censof for statistical analysis.

Laboratonal Analyses

Following microbiological analysis were performed for each sample: total plate count (PCA - Plate Count Agar, Merk, Germany) and lactic bacteria count (MRS - Lactobacilli MRS Agar, Acumedia, Michigan). pH and presence of viscosity were also determined in each sample.

Statistical Analyses

Statistical analyzes were performed using Statistica 7. 1 software. Survival analysis and Kaplan Meier estimator were used for evaluating of shelf-life.

RESULTS AND CONCLUSIONS

Samples were analyzed in determined time periods to detect the main microbiological, physicochemical and sensorial parameters involved in spoilage process during storage.

As it can be noticed by results, values tend to present the same behavior for all temperatures. Total plate counts, lactic bacteria counts and pH showed significant variation concerning storage time.

These results suggest that total plate counts are due to multiplication of lactic bacteria once values tended to present the same behavior. Lactic bacteria naturally inhabit the environment of cooked and refrigerated meat products packed under anaerobic conditions, as reported by Noskowa (1978), Giannuzzi et ah (1998), Sakala et al (2002), Blickstad et al. (1983), Von Holy et al. (1991) and Ferreira (2004).

According to Noskowa (1978), multiplication of lactic bacteria is due to the high carbohydrate content present in sausages. Such microorganisms present an irregular behavior regarding to its heat stability. By this way, if Noskowa' s approach would consider, it is possible that lactic acid bacteria survived to the process.

Cayré et ah (2005), also report such behavior, reinforcing the possibility of survival of these microorganisms to the cooking process due to the heat tolerance, besides being tolerant to NaCl, nitrite and cure process. Results obtained in the present work are in agreement with the findings presented by the cited authors and explain the post-processing multiplication during storage of sausages.

Also, it was observed a decreasing in pH values for both tests. According to Borch et al. (1996) and Metaxopoulus et al. (2002) lactic or acetic acid production by lactic acid bacteria explains such decreasing, observed in samples during storage.

The observed viscosity occurs due to the acid production by bacteria. Such viscosity that occurs out of products is positive in wet surfaces, typical environment of sausage packs. This occurrence makes evident an unpleasant aspect of the product to the consumer becoming a rejection parameter. These results are in agreement with Borch et cd. (1996).

The present work allow to clarify that it is possible to apply the survival analysis for studying shelf-life of food products, being possible to verify the probability of consumer to reject a product after a period of storage.

The fig. 1 shows product stored at 2°C, shelf-life is approximately 1,032 hours (43 days), product stored at 6.5°C, shelf-life is approximately 504 hours (21 days), product stored at 15°C, shelf-life is approximately 120 hours (5 days), product stored at 21°C, shelf-life is approximately 30 hours (1.25 days). However, it can be concluded that the statistical method used in the present work can provide storage options and probabilities data for survival of products presented to the consumers. It also allows to evaluate and to determine the real shelf-life of products that for some reason were stored at adverse conditions.

References

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