Microbial Growth in Ground Beef Throughout Different Methods of Thawing Saba ZahidTheodore Fleming*G. Kevin Randall*Bradley University

KEYWORDS: ground beef, microbial growth, food safety, time


Consumer safety and security has currently end up being a pressing worry through current illnesses and also food recalls as a result of elevated microbiologicalcontamicountry of a selection of different foods. Although tbelow are many type of various actions in the handling and also processingcontinuum that expose the food supply to potential microbial exposure and also contamicountry, consumers can limittheir danger for food-borne disease by practicing safe food managing practices in their dwellings. In this examine, weexamined several typically supplied thawing techniques and also their impact on microbial expansion.

The purpose of this research wregarding evaluate the influence of various thawing methods on microbial growth in groundbeef. Microbial expansion was evaluated throughout a six-hour thaw period utilizing three various thawing methods: refrigerator,room temperature, and also standing water bath. Beef preserved in the freezer was offered as a regulate. Bacterialcounts per gram of beef were established at one-hour intervals utilizing a viable count strategy.

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The leastern amount of bacterial growth occurred when beef was thawed in the refrigerator while bacterial growthemerged even more quickly in beef thawed at room temperature or in a standing water bath. After 6 hrs, beef thawed in a standingwater bath had actually the greatest bacterial count, 1.5 x 104 bacteria per gram of beef. This was 1.75 and 3.89 times greater thanthe microbial counts in beef samples thawed at room temperature or the refrigerator, respectively.


Food security is a peak priority for food organization organizations because misdealing with and also food spoilage deserve to resultin severe illnesses for consumers, in addition to obvious other business-related losses. Recently, many type of differentfood items have been recalled from the sector because of wide outbreak of illness resulted in by bacterial development. Groundbeef was just one of the food items redubbed (Sotos, 2008). Consumer safety has been lugged to the forefront withthese recent outbreaks.

An understanding of microbiology and also microbiological models are vital for implementing safe food processingand also taking care of steps. Models have the right to be provided to predict development, survival, or inactivation of microbes as a functionof affecting components (Marks, 2008). Temperature and also pH are among the determinants that have the right to impact microbial spoilageof ground beef. (Koutsoumanis, Nychas actually, Skandamis, & Stamatiou, 2006). Glucose and also sodium chloride concentrationsare various other determinants that influence microbial development (Koutsoumanis et al.; Marks).

Microbial expansion has been studied under various problems to formulate mathematical models that might be utilizedto predict microbial development. These models and predications have the right to then be provided in food processing. However, utilizationmay be restricted by uncertainty and variability of preparation conditions and accuracy of models (Marks, 2008).Different models have actually been designed and validated utilizing isothermal temperature conditions, non-isothermal problems,and also cooling duration temperatures after preparation of food (Corradini, Normand, Peleg, Schaffner, & SmithSimpboy, 2007; Koutsoumanis et al., 2006; Marks).

Although these microbiological models have actually been designed for utilization by food organization organizations, manyresearches usage specific and regulated temperature conditions to design models. Furthermore, ground beef sampleswere inoculated through bacterial strains cultivated in the lab quite than making use of bacterial samples normally grownin the ground beef (Corradini et al., 2007). I uncovered no researches incorporating the basic pointer thathigh-threat foodstuffs should not be out of storage temperatures for even more than 4 hrs.

The potential for microbial expansion or contamicountry can occur in many type of of the different areas of the ‘handlingcontinuum from “farm to table”’ (Black & Davidson, 2008, p. 163). At the consumer preparationlevel, there are likewise danger determinants that have the right to affect microbial exposure and also expansion. Temperature abusage in theresidential setting is a likely source of microbial growth and studies have shown that the refrigerator alonecan be a source of excellent temperature variation. Babsence and also Davidkid also cited cross-contamination and inadequatefood preparation of ground beef as major risk determinants of microbial expocertain. Although they did acknowledge temperaturevariations in the refrigerator, tright here was no literary works on various thawing approaches and their influence on microbialdevelopment in raw meat assets.

Thus, the objective of this research was to quantify the bacterial development in ground beef in the time of 4 commonlyoffered approaches of thawing. Growth was standardized per gram of ground beef and compared. The question was whichstrategy of thawing would certainly have actually the greatest amount of microbial growth in the time of the six-hour thawing duration. Thevarious thawing approaches carry out various temperature and moisture atmospheres, 2 components that influencethe development of microbes (Koutsoumanis et. al, 2006; Marks, 2008). Based on the literary works concerning factors ofmicrobial expansion, we hypothesized that the ground beef sample thawed in a room temperature water bath would certainly havethe greatest amount of microbial development while the sample thawed in the refrigerator would have the least amountmicrobial growth.


SampleFour (4) one-pound packeras of fresh ground beef werebought from a national chain grocery merchant and frozen for 3 days prior to testing. Each of the four packperiods wasbased on just one of the four conditions (freezer, water bath, room temperature, or refrigerator). All packages ofground beef were purchased within two days of their “offer by” days.

ProceduresDuring speculative thawing, packeras were hosted in the freezer (control), refrigerator,room temperature water bath, and also room temperature. Thaw temperatures were taken to verify temperature constancyfor each thaw method. In addition, the outsides of the beef packperiods were sterilized through a 70 percent ethanolsolution to remove contamicountry of the ground beef had within the packages. One-inch incisions weremade in the packaging to access the ground beef. The incisions were extended through sterile plastic wrap to preventecological contamination. Approximately one-gram samples were taken from each package at one-hour intervalsand also samples were diluted in nine milliliters of sterilized de-ionized water before being plated on NutrientAgar plates. Plates were incubated at 30° C for 48 hrs.

MeasuresAfter 48 hrs in the incubator, the numberof bacterial swarms on each agar plate were counted and used to calculate bacterial cells per gram of beeffor each sample.

Documents AnalysisThe calculated number of bacterial cellswas plotted in an excel graph versus time in hours (x-axis) for each of the thawing approaches. Using excel, aideal fit trendline was then added to the graph for each of corresponding sets of data for the thawing methods. Thesefinest fit lines represented the growth of bacteria in each of the samples over the six-hour trial and error duration.


The leastern amount of bacterial expansion arisen as soon as beef was thawed in the refrigerator while bacterial growthdeveloped even more quickly in beef thawed at room temperature or in a standing water bath. (These data astood for in Table 1.) After 6 hrs, beef thawed in a standing water bath had the biggest bacterial count,1.5 x 104 bacteria per gram of beef. This was 1.75 and also 3.89 times higher than the microbial counts in beef samplesthawed at room temperature or the refrigerator, respectively. Figure 1 reflects that the sample thawed in the waterbath had actually greatest rate of development. Ground beef held in the freezer (the control) had no measurable increase inbacterial cell number.

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Table 1: Bacterial cells per gram beef during various thawing methods at one-hour intervals

0 hours

1 hours

2 hours

3 hours

4 hours

5 hours

6 hours

Freezer (control)
























Room Temp








Figure 1: Rate of bacterial development in ground beef throughout various methods of thawing



Results evidenced the hypothesis that a room temperature water bath provided to thaw ground beef resulted in the greatestamount of microbial development during the six-hour thawing period. The rate of development was likewise greatest inthis sample. The sample thawed in the refrigerator had actually the leastern amount of microbial expansion.

Tbelow are no comparative information for this research that examined the price and also amount of microbial growth in groundbeef throughout different approaches of thawing. Bacterial numbers and also development prices were compared among the thawingapproaches (refrigerator, room temperature water bath, and at room temperature) and also to the regulate (freezer). Theinitial variety of bacteria per gram of beef was relatively low; yet expansion raised with time under alltechniques of thawing (family member to control). Data indicate that prices of bacterial expansion in ground beef increasedthrough both increased thaw temperature and time. Although published studies related to bacterial growth have beenconducted under dynamic temperature problems (Corradini et. al, 2007; Koutsoumanis et. al, 2006), no studieshave concentrated on specific time periods of development.

Interestingly, 2 of the 4 samples of ground beef had higher than zero bacterial cells per gram before thawing.However, a recent research conducted by Bosilevac, Guernini, Kalchayanand, & Kochmaraie (2009) uncovered that commercialground beef samples have the right to contain strains of Salmonellae, but the ubiquity is low. This may account forthe initial visibility of microbial cells in the ground beef. In this examine, the microbes were not established.

Although the sample thawed in the room temperature water bath had actually the greatest variety of microbial cells pergram of ground beef at the finish of the six-hour thawing duration, the data set had actually some outlier points, which affectedthe as a whole trfinish line and also misstood for the price of microbial expansion. In addition, the data collected fromthe sample thawed at room temperature included a far-reaching outlier information points, which additionally influenced its trendline. The price of growth might actually have been greater than represented by the line, and also this would certainly have beenstood for had actually the outlier been thrown out. However, it need to be detailed that at the end of the six-hour thaw strategy,the variety of microbes in the sample thawed in the room temperature water bath was still significantly greaterthan the number of microbes in the sample thawed at room temperature. The outlier was a lot of likely the resultof speculative error. One feasible resource of error may have been that the scalpel was also warm after being sterilizedonce it was offered to acquire the one-gram of ground beef from the sample. The greater temperature may actually havekilled some of the microbes in the ground beef that the sterilized scalpel contacted. This is an error that couldhave influenced all measurements. Furthermore, it must be noted that while it has been proclaimed that moisture influencesdevelopment, the humidity of the room and also level of moisture in the refrigerator were not measured or necessarily controlled.

Although this study gave information under variable problems of temperature and also time, we conducted onlyone trial because of limited time and also sources. This is a significant limitation of the research. Future researches shouldconduct multiple trials to replicate our results and also show relicapacity of speculative actions and implementation.This study was likewise restricted because no literature was discovered regarding “acceptable” or safe levelsof microbial contamicountry so it is difficult to put the results right into perspective. Beef samples usedin this study had actually 80/20 composition (20 percent fat). Future study can explore the effect of fat percenton the microbial expansion throughout different thaw techniques. Another area that could be explored is the relationshipin between various kinds of packaging (i.e., plastic tube vs. Styrofoam plate and also plastic wrap) and the rate oramount of microbial growth in the time of thawing. An exciting application of this study may be its pairing with studiesthat research how a lot of a microbial population is “cooked out” during preparation. The level ofdoneness (i.e., rare, medium, well done) and also the variety of microbial cells continuing to be in the ground beef couldbe a room of future study. Although this research had actually its restrictions, it provides handy indevelopment around microbialexpansion in a “real-life” environment. The outcomes of this study add to the expertise base of consumersafety and security and the literary works of customer food safety and security techniques.