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Mikrobiologiska skillnader vid tillagning av kött med tre olika varianter av sous vide

Kodipelli Arachige Don, Daniel LU and Arvén, Alexander (2017) YTHL01 20171
Food Technology and Nutrition (M.Sc.)
Abstract
Sous vide is a cooking technique where ingredients are vacuum packed in a bag and then cooked in a waterbath, the temperature of which sous vide is used is often lower than the temperature used for traditionally cooked food. Foods cooked with sous vide usually have a higher quality when it comes to taste, as well as a longer shelf life than food cooked with traditional methods.

Since many home cooks don’t a have vacuum machine, other methods such as Ziplock bags or open bag are used. Packing the food into ziplock bags and closing them doesn't give a vacuum, this allows for aerobic bacteria to grow when air is available.

Although the method has existed and knowledge has spread, it’s in recent years the restaurant industry has come... (More)
Sous vide is a cooking technique where ingredients are vacuum packed in a bag and then cooked in a waterbath, the temperature of which sous vide is used is often lower than the temperature used for traditionally cooked food. Foods cooked with sous vide usually have a higher quality when it comes to taste, as well as a longer shelf life than food cooked with traditional methods.

Since many home cooks don’t a have vacuum machine, other methods such as Ziplock bags or open bag are used. Packing the food into ziplock bags and closing them doesn't give a vacuum, this allows for aerobic bacteria to grow when air is available.

Although the method has existed and knowledge has spread, it’s in recent years the restaurant industry has come across lab equipment to be able to cook sous vide in restaurants. The sous vide trend amongst home cooks is non-existing before the forum thread on eGullet. The forum thread sparked the trend. The knowledge exchange on eGullet have affected both home cooks and professionals, more restaurants use the sous vide technique and home cooks have also adapted to the technique.

The main goal of this study is to investigate the microbiological quality of beef prepared sous vide at 54 °C, according to three different variants of sous vide. The different variants mean that the meat is packed before cooking in three different ways, in a vacuum bag, in a Ziplock bag and in an open bag. The purpose is also to investigate whether the pre-treatment of the meat before it is placed in the bag affects the microbial status. The pre-treatments chosen are no pre-treatment, ie raw meat, a gas-fired surface and a dry salting of meat.

All tests were done twice. For each try, beef was divided into 27 pieces. Three different types of bags were tested with three different pre-treatments. The meat was browned with a gas burner to get a quick and intense heat, the fast heat was used to kill bacteria on the surface with such little cooking of the meat inside the surface as possible. Salt inhibits bacterial growth for some bacteria, therefore the meat is salted. 2% salt in relation to the meat weight was used. The untouched got no pre-treatment. The meat was cooked at 54 °C until the meat reached an internal temperature of 54 °C.

After cooking, half of the bags were stored for one week in a refrigerated room. Remaining bags were tested after the cooling down. The meat was cut and homogenized with peptone water. The samples were diluted to get readable results. Samples were put on both TSA and VRBD agar. The samples were grown and read. The PCR technique was used to distinguish which bacteria were grown. The bacterial colonies were separated and analyzed. Gas measurements were made in the bags to see how a change occurred in the bag.

When cooking the "sous vide" method without proper vacuum, the ingredients can be exposed to significantly more bacteria, as there is access to oxygen. The result of the gas analysis shows that a larger change occurs in the open bag against the ziplock bag after storage, due to the aerobic respiration that the bacteria conveys in the open bag.
During the tests no pathogenic bacteria were found, most were apathogenic, some may cause infections in people with impaired immune system. Some bacteria that were found would cause food degradation. The result differs slightly between all methods, however we see that the method where the surface is browned and the use of a vacuum bag has the greatest killing of bacteria and least growth after storage. (Less)
Popular Abstract (Swedish)
Sous vide går ut på att råvarorna vakuumförpackas i påse för att sedan tillagas i den förslutna påsen vid en temperatur lägre än vad som traditionellt används. Livsmedel som tillagas med sous vide har vanligtvis en bättre smakmässig kvalitet samt en längre hållbarhet än livsmedel som tillagats med traditionella metoder.

Många hemmakockar saknar vakuummaskin och tar istället till andra metoder som t.ex. ziplock-påsar eller öppen påse. Att packa livsmedlet i ziplock-påsar och försluta dessa ger inget vakuum, vilket då ger möjlighet för aeroba bakterier att växa då luft finns tillgängligt.

Även om metoden funnits och kunskapen sprids så är det på senare år som restaurangbranschen i en större skala kommit över labbutrustning för att... (More)
Sous vide går ut på att råvarorna vakuumförpackas i påse för att sedan tillagas i den förslutna påsen vid en temperatur lägre än vad som traditionellt används. Livsmedel som tillagas med sous vide har vanligtvis en bättre smakmässig kvalitet samt en längre hållbarhet än livsmedel som tillagats med traditionella metoder.

Många hemmakockar saknar vakuummaskin och tar istället till andra metoder som t.ex. ziplock-påsar eller öppen påse. Att packa livsmedlet i ziplock-påsar och försluta dessa ger inget vakuum, vilket då ger möjlighet för aeroba bakterier att växa då luft finns tillgängligt.

Även om metoden funnits och kunskapen sprids så är det på senare år som restaurangbranschen i en större skala kommit över labbutrustning för att kunna genomföra tillagning på restauranger. För hemmakockar talas det om före och efter forumtråden på eGullet, innan var den icke existerande och efter har trenden kring sous vide startat för hemmakockar. Kunskapsutbytet på eGullet berör både hemmakockar och professionella, fler restauranger använder metoden och hemmakocken anammar även de metoden.

Studien går ut på att undersöka den mikrobiologiska kvaliteten på biff som tillagats i vattenbad vid 54 °C enligt tre olika varianter av sous vide. De olika varianterna innebär att köttet förpackats innan tillagning på tre olika sätt, i vakuumpåse, i Ziplock-påse och i öppen påse. Syftet är också att undersöka om förbehandling av köttet innan det läggs i påsen påverkar den mikrobiella statusen. De förbehandlingar som valts är ingen förbehandling, alltså helt rått kött, gasolavbränd yta och torrsaltning av kött.

Testerna gjordes två gånger. Till varje försök användes biff som delades i 27 bitar. Tre olika påstyper testades, med tre olika behandlingar. Köttet bryntes med en gasbrännare för att få en snabb och intensiv värme, den snabba värmen användes för att avdöda bakterier på ytan med en så liten tillagning av köttet innanför ytan. Salt hämmar bakterietillväxten för vissa bakterier, därför saltades köttet. 2% salt i förhållande till köttets vikt användes. Den orörda fick ingen förbehandling. Köttet värmebehandlades på 54 °C tills köttet uppnått en innertemperatur på 54 °C.

Efter tillagningen lagrades hälften av påsarna i en vecka i kylrum. Resterande påsar testades efter nedkylning. Köttet skars upp och homogeniserades med peptonvatten. Proverna spädes för att kunna få läsabara resultat. Proverna sattes på både TSA- och VRBD-agar. Proverna odlades och lästes av. PCR-tekniken användes för att för att kunna urskilja vilka bakterier som vuxit. Bakteriekolonierna separerades och analyserades. Gasmätningar gjordes i påsarna för att kunna se om en förändring skett i påsen.

Vid tillagning med ”sous vide” metoden utan ordentligt vakuum kan produkten utsättas för betydligt flera bakterier, då det finns tillgång till syre. I resultatet från gas-analysen syns att en större förändring sker i den öppna påsen gentemot ziplockpåsen efter lagring, detta beror på den aeroba respirationen som bakterierna medför i den öppna påsen.

Under försöken hittades inte några patogena bakterier utan de flesta var apatogena, men några kan skapa infektioner hos personer med nedsatt immunförsvar. En del bakterier var förruttnelsebakterier. Resultatet skiljer sig lite mellan alla metoder, dock ser vi att metoden där ytan bryns och användandet av vakuumpåse med fullt vakuum har störst avdödning av bakterier samt minst tillväxt efter lagring. (Less)
Please use this url to cite or link to this publication:
author
Kodipelli Arachige Don, Daniel LU and Arvén, Alexander
supervisor
organization
course
YTHL01 20171
year
type
M1 - University Diploma
subject
keywords
mikrobiologisk avdödning, sous vide, avdödningseffekt, livsmedelsteknik
language
Swedish
id
8915311
date added to LUP
2017-06-29 09:07:42
date last changed
2017-06-29 09:07:42
@misc{8915311,
  abstract     = {Sous vide is a cooking technique where ingredients are vacuum packed in a bag and then cooked in a waterbath, the temperature of which sous vide is used is often lower than the temperature used for traditionally cooked food. Foods cooked with sous vide usually have a higher quality when it comes to taste, as well as a longer shelf life than food cooked with traditional methods.

Since many home cooks don’t a have vacuum machine, other methods such as Ziplock bags or open bag are used. Packing the food into ziplock bags and closing them doesn't give a vacuum, this allows for aerobic bacteria to grow when air is available.

Although the method has existed and knowledge has spread, it’s in recent years the restaurant industry has come across lab equipment to be able to cook sous vide in restaurants. The sous vide trend amongst home cooks is non-existing before the forum thread on eGullet. The forum thread sparked the trend. The knowledge exchange on eGullet have affected both home cooks and professionals, more restaurants use the sous vide technique and home cooks have also adapted to the technique.

The main goal of this study is to investigate the microbiological quality of beef prepared sous vide at 54 °C, according to three different variants of sous vide. The different variants mean that the meat is packed before cooking in three different ways, in a vacuum bag, in a Ziplock bag and in an open bag. The purpose is also to investigate whether the pre-treatment of the meat before it is placed in the bag affects the microbial status. The pre-treatments chosen are no pre-treatment, ie raw meat, a gas-fired surface and a dry salting of meat.

All tests were done twice. For each try, beef was divided into 27 pieces. Three different types of bags were tested with three different pre-treatments. The meat was browned with a gas burner to get a quick and intense heat, the fast heat was used to kill bacteria on the surface with such little cooking of the meat inside the surface as possible. Salt inhibits bacterial growth for some bacteria, therefore the meat is salted. 2% salt in relation to the meat weight was used. The untouched got no pre-treatment. The meat was cooked at 54 °C until the meat reached an internal temperature of 54 °C.

After cooking, half of the bags were stored for one week in a refrigerated room. Remaining bags were tested after the cooling down. The meat was cut and homogenized with peptone water. The samples were diluted to get readable results. Samples were put on both TSA and VRBD agar. The samples were grown and read. The PCR technique was used to distinguish which bacteria were grown. The bacterial colonies were separated and analyzed. Gas measurements were made in the bags to see how a change occurred in the bag.

When cooking the "sous vide" method without proper vacuum, the ingredients can be exposed to significantly more bacteria, as there is access to oxygen. The result of the gas analysis shows that a larger change occurs in the open bag against the ziplock bag after storage, due to the aerobic respiration that the bacteria conveys in the open bag.
During the tests no pathogenic bacteria were found, most were apathogenic, some may cause infections in people with impaired immune system. Some bacteria that were found would cause food degradation. The result differs slightly between all methods, however we see that the method where the surface is browned and the use of a vacuum bag has the greatest killing of bacteria and least growth after storage.},
  author       = {Kodipelli Arachige Don, Daniel and Arvén, Alexander},
  keyword      = {mikrobiologisk avdödning,sous vide,avdödningseffekt,livsmedelsteknik},
  language     = {swe},
  note         = {Student Paper},
  title        = {Mikrobiologiska skillnader vid tillagning av kött med tre olika varianter av sous vide},
  year         = {2017},
}