Detection of Listeria in ice cream Essay


Listeriasis a psychrophile and ice-cream is extremely alimentary complete dairy based nutrient stored in stop deading or refrigerated conditions unless consumed. Detection for theListeriasspp. from the ice-cream sample was performed from 20 different Ice-cream samples. From these, two samples showed presence ofListeriassps. based on cultural, morphological, biochemical and physiological trials. Of these two isolates, one was taken and D50°CValue and consequence of preservatives were determined. D50°CValue was determined to be 41 proceedingss with lessening rate – 0.07011 log10CFU per minute being 4.42 times quicker than the regular addition rate of 0.016525 log10CFU per minute at favourable incubation conditions at 25°C. Both of the preservatives were found out to be bactiostatic in action, and of the two preservatives, benzoic acid was found out to be the better preservatives than K nitrate. The growing rate was found to diminish extensively 5.3 times less utilizing K nitrate and 6.3 times utilizing Na benzoate than without utilizing any preservatives.

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KEYWORDS:Listerias, D-Value, Preservatives, Ice-cream, Prakash


Harmonizing to Subarna M. Pradhan, 2005, ice pick is an emerging dairy merchandise in Nepal. Ice pick parlor are going common in major metropoliss. Estimated one-year ice pick production from DDC and private sector is about 1,000 dozenss and the chief market is Kathmandu vale and Pokhara. Eighty three per centum of ice pick production is in the private sector followed by imported trade names from India.

Ice-cream represents a jelled dairy merchandise produced by stop deading a pasteurised mixture of milk, pick, milk solids other than fat, sugars, emulsifier and stabilizers ( FEHD, HKSAR, 2001 ) . Ice pick as defined by The Food And Drug Administration ( FDA, 2003 ) , “is a nutrient produced by stop deading, while stirring, a pasteurised mix dwelling of one or more of the optional dairy ingredients specified in paragraph ( B ) of this subdivision, and may incorporate one or more of the optional caseinates specified in paragraph ( hundred ) of this subdivision topic to the conditions here in after set Forth, one or more of the optional hydrolyzed milk proteins as provided for in paragraph ( vitamin D ) of this subdivision topic to the conditions hereinafter set Forth, and other safe and suited non milk-derived ingredients ; and excepting other nutrient fats, except such as are natural constituents of seasoning ingredients used or are added in incidental sums to carry through specific maps. With all ingredients, ice- pick is a complete nutrient, therefore can move as a complete medium for the proper growing and development of the micro-organisms. Added to that if stored in cold conditions and micro-organisms are present, they can stay feasible but merely metabolically hibernating.

Listeria monocytogenesis a Gram-positive bacteria that occurs widely in both agricultural ( dirt, flora, silage, fecal stuff, sewerage, H2O ) , aquicultural, and nutrient processing environments.L. monocytogenesis a ephemeral occupant of the enteric piece of land in worlds, with 2 to 10 % of the general population being bearers of the micro-organism without any evident wellness effects. Although often present in natural nutrients of both works and animate being beginning, sporadic instances or eruptions of listeria meningitis are by and large associated with ready-to-eat, refrigerated nutrients, and frequently involves the station processing recontamination of cooked nutrients ( CAC, 2007). Similar toL. monocytogenes,L.ivanoviiis besides a possible menace to people with impaired unsusceptibility, and largely pregnant adult females are the closest categorized into menace ( CDC, 2010 ) . Cell wall composings ofListeriasspp. show peptidoglycan, teichoic acids, lipoteichoic acids and more-or-less comparable to other Gram positive bacteriums. But, one of the most confusing characters while detecting under microscope is that they appear otherwise. Though Gram positive rods, they show variable Gram reaction, as when observed under microscope non clearly seen as rods. Sometimes they are confused with cocci in agreements like diplococci, and some other clip they appear to be rods arranged in angles, and some other times as individual rods excessively. Therefore, they don’t have that clear agreements and they don’t show that clear Gram’s reaction ( Goldfineet Al., 2007 ; Garrityet Al., 1984 ) . They show umbrella like motility in Listeria motility agar, show actin-based motility, are oxidase negative, most are catalase positive. These are esculin positive, non-pigmented, but show blue shininess at Henry’s angle at 10 Ten glass phase Microscope.Listeria monocytogeneswas foremost isolated in 1918 from cerebrospinal fluid ( meningitis ) of a soldier. 1926: Sudden decease of immature coneies ; mononucleate leukocytosis ; documented isolation ( Murray et al. ) ofBacterium monocytogenes.In 1940: named after Joseph Lister ; “Listeria monocytogenes”. In 1979, these were identified to be the emerging nutrient borne pathogens. In 1980s, legion eruptions were faced due toListeria monocytogenes( USDA-FSIS, 2006 ) . All together there are merely six species ofListerias;L. monocytogenes,L. innocua,L. welshimeri,L. seeligeri,L.ivanoviiandL. grayi. Of these all, the lone pathogenic strain to homo isListeria monocytogenes. They are chiefly of two types, haemolytic and non-hemolytic. Even withinListeria monocytogenesthere are different strains which appear to be haemolytic and some others non haemolytic. Hemolysis in Blood agar or any chromogenic agar is designed to observe the production of the Listeriolysin-O. This Listeriolysin-O is responsible for the break of the phagolysosome membrane and so it is the major virulency factor ofL. monocytogenes( Colleeet Al., 2006 ) .L. monocytogeneshas 13 known serovars, but four of them ( 1/2a, 1/2b, 1/2c, and 4b ) are responsible for over 95 % of reported human listeria meningitis instances, and major eruptions of listeria meningitis have been caused byL. monocytogenes4b ( USDA, 2007 ) .

No elaborate survey onListeria monocytogeneshave been performed in any nutrient merchandises of Nepal. This survey focuses the current state of affairs and being ofListeriasspecies in ice-cream and besides towards the control of the strayListeriasspecies by temperature or with the usage of preservatives.


Sample aggregation was done by utilizing the sealable-pouches. The sealable pouches had foremost been treated with intoxicant and hot-air-oven dried at really low temperature of around 30°C, wrapped in the aluminium foil. All samples were collected in early forenoon clip, and were reached to lab every bit shortly as possible. At one clip five different samples were collected in separate disinfected pouches, and labeled every bit shortly as collected. Sample aggregations were done in the general mode in which the sample were sold. The sample was straight received into the pouches, the status they are given or served to the local clients. All of the samples in pouches were kept in Ice-box, so that it won’t addition heat. Equally shortly as making the lab the samples were once more kept at deep-freezing temperature ( -18°C ) boulder clay sample is processed.

All together 20 different samples were collected and duplicate sampling was done. Based on settlement morphology one hundred and eleven different settlements were taken from home base count agar after pour plating. The settlements so ascertained were so farther enriched inListeriasenrichment stock and plated each by each onListeriasselective agar. By this, 79 different isolates were determined to be more proximatelyListeriasin visual aspect. Of these, farther trial with esculin hydrolysis showed merely 62 isolates more close to beListeriasspecies. With late gm positive, catalase positive and oxidase negative reactions ; merely 36 different isolates were more close to beListeriasspecies. With biochemical and cultural characters as methyl ruddy positive/negative, voges proskauer positive, ternary sugar Fe agar acid/ acid, and typical characters onListeriaschromogenic agar, ( rhamnose positive and glucosidase positive ) andListeriasmotility agar 19 ( umbrella-like motility ) different settlements were so undergone the carbohydrate agitation trials for verification with concluding five different proximate isolates. These isolates were so farther undergone urease trial for negative consequences and so slant agar of tryptone soy agar for bluish sheen settlements. And eventually two of the entire isolates were determined to be theListeriasspecies.

Of all five proximate isolates,Listeriasspecies i3was processed for the finding of D-value and consequence of the preservatives. D-value was determined at 50 EsC utilizing waterbath with shaker ( unfertile conditions maintained ) and so numbering at zeroth and regular clip intervals.

For the finding of the consequence of preservatives with K nitrate and Na benzoate, the Log10CFU alteration with regard to clip and preservative being used in fresh milk with mention criterions of K nitrate and Na benzoate were determined, incubated at optimal 25 EsC in H2O bath with shaker ( unfertile conditions maintained ) .


D-value was determined to be fourty-one proceedingss at 50 EsC. Consequence of K nitrate was found to be more distinguishable than that of Na benzoate, with growing rate in milk with K nitrate ( 30mg/lit ) , with Na benzoate ( 450 mg/lit ) , and without any preservatives severally being 0.001988889 log10CFU per minute, 0.001677778 log10CFU per proceedingss and 0.010592222 log10CFU per minute.

CONCLUSION ( Optional )



A upper limit of 25 mentions

Citation: Enumeration. Vancouver Style ; Example: Writer ( Gupta A.K. ) , Paper rubric, Journal name, Volume, Issue, Date, Pages, ISSN


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