Effects Of Natural Plant Extracts On Inhibition Of Listerial Monocytogenes And On Quality Attributes Of Frankfurters

Because the concepts of "Natural" and "Organic" are more and more popular among consumers, these natural and organic food products have experienced rapid growth all around the world. However, due to the regulations of "Natural product" in the US, sodium nitrite is not allowed to be used in manufacturing cured meat products. Many meat processors started to use celery powder to replace direct addition of sodium nitrite or sodium nitrate. These "naturally cured" meat products may be more susceptible to the growth of food borne pathogen due to its unstable sauce of nitrite. To meet the regulations of "Natural" product, several natural ingredients were selected in this research to evaluate its ability to inhibite Listeria monocytogenes growth in both the meat model system and the naturally cured frankfurter, and also the effectiveness on quality and sensory attributes of the frankfurters.This research contained two studies:the model system study and the meat product study. The meat model system was designed to closely resemble commercial frankfurters. Several natural ingredients were included in the model system and Listeria monocytogenes was inoculated. The objectives of the model system study were to investigate:(Ⅰ) the ability of selected natural ingredients alone or in combination to inhibit L. monocytogenes in a cured and cooked meat model system; and (Ⅱ) assess the changes of nitrite in the meat model system when combined with these natural plant and fruit ingredients. The second study was based on the results of the model system study. Its objectives were to investigate: (1) the ability of selected natural ingredients to inhibit L. monocytogenes growth on inoculated naturally-cured frankfurters during refrigerated storage; (2) the effects of selected natural ingredients on physical and chemical characteristics of naturally-cured frankfurters including color, texture, lipid oxidation and residual nitrite during storage; (3) the sensory attributes of naturally-cured frankfurters that may be affected by the ingredients selected for potential antilisterial effects. It was expected to find one or two natural ingredients alone or in combination that would be inhibitory to Listeria monocytogenes without negatively impact the quality and sensory attributes of the products.1. Inhibitions of different ingredients to Listeria monocytogenes growth in the cured and cooked meat model systemIngoing nitrite of 150 mg/kg was confirmed as important for improving control of Listeria monocytogenes. Although it can not fully inhibit this pathegon, it can increase the lag phase and slow the growth of Listeria monocytogenes. Traditional antimicrobials such as lactate and diacetate were also confirmed as effective L. monocytogenes inhibitors, but their status with the USDA as permitted ingredients in manufacturing natural and organic meat products is still unclear. Lactate at 2% and 4.8%, diacetate at 0.25% significantly reduced the growth of L. monocytogenes by 2-5 log 10 cfu/g (P<0.05). Cranberry powder also showed significant inhibition to L. monocytogenes due to its rich amount of polyphenolic compounds and low pH. Cranberry powder at 1-3% significantly inhibited L. monocytogenes growth by 2-4 log 10 cfu/g (P<0.05). Other selected natural compounds, such as cherry powder, lemon powder, lime powder, and grape seed extract, were less effective, but may still have potential to improve the control of L. monocytogenes when combined with cranberry powder. Especially cranberry and cherry combination could increase nitrite reaction rates and affect antimicrobial impact in natural and organic meat products.2. Effects of different ingredients on residual nitrite changes during storage in cured and cooked meat model systeOver 50% of ingoing nitrite was depleted following heating. The amount of nitrite decreased during the storage period. Diacetate resulted in significant less residual nitrite than lactate, and reduced residual nitrite concentration by 23 mg/kg on day 12 (P<0.05). Cherry powder is a natural source of ascorbic acid and may serve as a natural reductant for nitrite in natural and organic cured meat products by enhancing nitrite curing reactions and reducing residual nitrite level. Cherry powder at 0.6% significantly decreased residual nitrite level by 30 mg/kg on day 12 compared to the control (P<0.05), which was not significantly different from the residual nitrite concentration of treatment SA (P>0.05). Cranberry powder also showed significant reducing activity to nitrite due to its rich amount of polyphenolic compounds and low pH. Cranberry powder at 1-3% had significant less residual nitrite of 18-63 mg/kg compared to the control (P<0.05). Other selected natural compounds, such as lemon powder, lime powder, and grape seed extract, did not result in significant nitrite reduction, but may still have potential to facilitate curing reactions when combined with cranberry powder. Cranberry and cherry powder may function as natural antimicrobial and reductant in natural and organic cured meat products to improve the shelf life of these products.3. Effects of natural ingredients on inhibition of Listeria monocytogenes and on chemical, physical and sensory attributes of frankfurtersNatural antimicrobials utilized in manufacturing of the naturally-cured frankfurters have potential to affect the chemical, physical and sensory attributes of the finished products. In this study, the addition of cranberry powder at 1-3% significantly reduced the growth of inoculated L. monocytogenes by 2-4 log 10 cfu/g (P<0.05), but at concentrations over 1% resulted in significant pH decline by 0.2-0.8 unit (P<0.05), creating a negative impact on the sensory quality attributes including cured color, flavor and aroma, and softer texture. The cranberry treatments resulted in significant lower residual nitrite concentrations during storage compared to other treatments (P<0.05). The higher level of cranberry added, the less residual nitrite in the products detected. No significant difference in TAB values were found between the cranberry treatments and the naturally-cured control (P>0.05). The lower level of cranberry powder (≤1%) may be considered to enhance the antibacterial quality and shelf life in naturally-cured meat products because the quality effects were not as dramatically affected at this concentration. However, the impact of cranberry powder to sensory quality attributes of processed meats is an important consideration that should be taken into account before the antimicrobial properties of the cranberry powder can be effectively utilized.