Effect of Filling Type and Heating Method on Prevalence of Listeria species and Listeria monocytogenes in Dumplings Produced in Poland Barbara Szymczak and Waldemar Da˛browski
M: Food Microbiology & Safety
Abstract: The count of Listeria monocytogenes was determined, before and after heat treatment, in 200 samples of dumplings of 9 brands and with different types of stuffing. Analyses were conducted according to ISO 11290–1 standard and with real-time PCR method. The highest count of L. monocytogenes was found in meat dumplings (102 to 104 CFU/g), whereas products with white cheese-potato stuffing and vegetable-mushroom stuffing contained significantly less Listeria, 20 to 80 and 5 to 32 CFU/g, respectively. In cooled meat dumplings the extent of contamination depended significantly on the producer. In addition, a significant (P < 0.05) correlation was determined between contamination level and meat content in the stuffing (rho = 0.418), especially in stuffing containing pork meat (0.464), contrary to beef-containing stuffing (0.284). Heating dumplings in boiling water for 2 min completely eliminated L. monocytogenes in meat dumplings. In contrast, the microwave heating applied for 2 min at 600 W only reduced the count of L. monocytogenes by 1 to 2 logs. Hence, the microwave heating failed to reduce the risk of infection with this pathogen below the level permissible in the EU regulation, especially in the most contaminated samples. In this case, the efficacy of microwave heating was significantly (P < 0.05) affected by the initial count of L. monocytogenes (rho = 0.626), then by meat content in the stuffing (0.476), and to the lowest extent—by the type of meat (0.415 to 0.425). However, no Listeria sp. and L. monocytogenes were isolated from cooked dumplings with fruits (strawberries or blueberries). Keywords: dumplings; Listeria monocytogenes, Listeria sp., meat, microwave heating, real-time PCR
Practical Application: Results achieved provide valuable information to producers and consumers of dumplings regarding the possibility of L. monocytogenes survival during cooking in water and heating in a microwave oven. Results were presented to food producers and works are in progress on establishing safe method of heating that would be recommended on unitary packages.
Introduction
onions, and spices. In Chile, there are pantrucas, a type of flat, elongated irregular dumplings flavored with fresh parsley and served in soup. Depending on the country and culture, dumplings are consumed in different forms, with different types of stuffing and additives. In Poland, dumplings are a popular dinner dish consumed by all social groups at home and restaurants. They are increasingly often bought owing to easy, convenient, and fast preparation before consumption and low price. In the food industry, dumplings are precooked, cooled, and packed into plastic packages. Before consumption, they only need to be warmed-up. Until recently, heat treatment of dumplings involved only cooking and warming-up in boiling water. However, consumers’ need for short and convenient preparation, dumplings are increasingly often heated in domestic microwave ovens. Stuffing of dumplings is produced from: (i) meat, (ii) vegetables with mushrooms, (iii) white cheese with potatoes, or (iv) fruits (seasonal dumplings). So far, there is no report in the literature concerning foodborne infections caused directly by the consumption of dumplings. However, the stuffing contains high amount of meat, cheese, fruits, or vegetables that may be contaminated with: Listeria monocytogenes, as these ingredients have been linked MS 20141851 Submitted 11/6/2014, Accepted 1/15/2015. Authors are with Dept. of Microbiology and Applied Biotechnology, West Pomeranian Univ. of Technol- to many cases of foodborne listeriosis. Criteria for L. monocytogenes are specified in Commission Regogy, Papie˙za Pawła VI 3 st., 71-459, Szczecin, Poland. Direct inquiries to author Szymczak (E-mail: [email protected]). ulation on Microbiological Criteria for foodstuffs (EC 2005). The Dumplings are food products made of a piece of thin dough (water and wheat flour, often with the addition of egg and oil) filled with different types of stuffing. Before consumption, dumplings require heat treatment via warming-up, cooking or roasting. The recipe of dough for various dumplings is very similar, but what they differ in is mainly the type of stuffing. Usually, dumplings are half-moon shaped and weigh 15 to 25 g, which constitutes 80% to 90% of dumpling weight, depending on producer and type of stuffing. Dumplings are known all over the world. In Ukraine, Belarus, Lithuania, and Russia different types of dumplings are called: pielmienie, czebureki, cepeliny, kibiny, kołduny, and so on. Chinese dumplings include: wonton, guo tie, or jiaozi. Italian dumplings include: ravioli and tortellini, whereas in Germany popular dumplings with white cheese, meat, or vegetable stuffing are called Maultaschen. Savory dumplings made from balls of dough are part of traditional British and Irish cuisine. In Brazil, there are pastels, coxinhas, and bolinhas de carne which are fried dumplings filled with chicken, pork, or beef mixed with olives,
M1060
Journal of Food Science r Vol. 80, Nr. 5, 2015
R C 2015 Institute of Food Technologists
doi: 10.1111/1750-3841.12816 Further reproduction without permission is prohibited
L. monocytogenes in dumplings . . . Table 1–Occurrence of Listeria monocytogenes in dumplings. Contamination with L. monocytogenes [CFU/g]
Type of stuffing in dumplings Meat Vegetablemushroom
White cheese-potato Fruit Total:
Ingredients stuffing Pork and beef, fat, onion, salt, pepper Fermented savoy cabbage, carrot, wild mushrooms, onion, oil, salt, pepper White cheese, potatoes, onion, salt, pepper Strawberries, sugar Blueberries, sugar 9 (A–I)
Number of analyzed producers
Number of analyzed samples
Number of positive samples (% of positive samples before heating)
8 (A–H)
66
6 (A–F)
After cooking in boiling water
Before heating
After microwave heating
35 (53.0)
3 × 102 to 1.4 × 104
0 to 2.7 × 103
03
11
2 (18.2)
5 to 32
nb1
nb1
6 (A–F)
23
4 (17.4)
20 to 80
nb1
nb1
1 (I)
60 40 41 (20.5%)
nb2 nb2 –
nb2 nb2 –
nb2 nb2 0
0 0
200
nb —not analyzed, because the level of contamination reached
M: Food Microbiology & Safety
Abstract: The count of Listeria monocytogenes was determined, before and after heat treatment, in 200 samples of dumplings of 9 brands and with different types of stuffing. Analyses were conducted according to ISO 11290–1 standard and with real-time PCR method. The highest count of L. monocytogenes was found in meat dumplings (102 to 104 CFU/g), whereas products with white cheese-potato stuffing and vegetable-mushroom stuffing contained significantly less Listeria, 20 to 80 and 5 to 32 CFU/g, respectively. In cooled meat dumplings the extent of contamination depended significantly on the producer. In addition, a significant (P < 0.05) correlation was determined between contamination level and meat content in the stuffing (rho = 0.418), especially in stuffing containing pork meat (0.464), contrary to beef-containing stuffing (0.284). Heating dumplings in boiling water for 2 min completely eliminated L. monocytogenes in meat dumplings. In contrast, the microwave heating applied for 2 min at 600 W only reduced the count of L. monocytogenes by 1 to 2 logs. Hence, the microwave heating failed to reduce the risk of infection with this pathogen below the level permissible in the EU regulation, especially in the most contaminated samples. In this case, the efficacy of microwave heating was significantly (P < 0.05) affected by the initial count of L. monocytogenes (rho = 0.626), then by meat content in the stuffing (0.476), and to the lowest extent—by the type of meat (0.415 to 0.425). However, no Listeria sp. and L. monocytogenes were isolated from cooked dumplings with fruits (strawberries or blueberries). Keywords: dumplings; Listeria monocytogenes, Listeria sp., meat, microwave heating, real-time PCR
Practical Application: Results achieved provide valuable information to producers and consumers of dumplings regarding the possibility of L. monocytogenes survival during cooking in water and heating in a microwave oven. Results were presented to food producers and works are in progress on establishing safe method of heating that would be recommended on unitary packages.
Introduction
onions, and spices. In Chile, there are pantrucas, a type of flat, elongated irregular dumplings flavored with fresh parsley and served in soup. Depending on the country and culture, dumplings are consumed in different forms, with different types of stuffing and additives. In Poland, dumplings are a popular dinner dish consumed by all social groups at home and restaurants. They are increasingly often bought owing to easy, convenient, and fast preparation before consumption and low price. In the food industry, dumplings are precooked, cooled, and packed into plastic packages. Before consumption, they only need to be warmed-up. Until recently, heat treatment of dumplings involved only cooking and warming-up in boiling water. However, consumers’ need for short and convenient preparation, dumplings are increasingly often heated in domestic microwave ovens. Stuffing of dumplings is produced from: (i) meat, (ii) vegetables with mushrooms, (iii) white cheese with potatoes, or (iv) fruits (seasonal dumplings). So far, there is no report in the literature concerning foodborne infections caused directly by the consumption of dumplings. However, the stuffing contains high amount of meat, cheese, fruits, or vegetables that may be contaminated with: Listeria monocytogenes, as these ingredients have been linked MS 20141851 Submitted 11/6/2014, Accepted 1/15/2015. Authors are with Dept. of Microbiology and Applied Biotechnology, West Pomeranian Univ. of Technol- to many cases of foodborne listeriosis. Criteria for L. monocytogenes are specified in Commission Regogy, Papie˙za Pawła VI 3 st., 71-459, Szczecin, Poland. Direct inquiries to author Szymczak (E-mail: [email protected]). ulation on Microbiological Criteria for foodstuffs (EC 2005). The Dumplings are food products made of a piece of thin dough (water and wheat flour, often with the addition of egg and oil) filled with different types of stuffing. Before consumption, dumplings require heat treatment via warming-up, cooking or roasting. The recipe of dough for various dumplings is very similar, but what they differ in is mainly the type of stuffing. Usually, dumplings are half-moon shaped and weigh 15 to 25 g, which constitutes 80% to 90% of dumpling weight, depending on producer and type of stuffing. Dumplings are known all over the world. In Ukraine, Belarus, Lithuania, and Russia different types of dumplings are called: pielmienie, czebureki, cepeliny, kibiny, kołduny, and so on. Chinese dumplings include: wonton, guo tie, or jiaozi. Italian dumplings include: ravioli and tortellini, whereas in Germany popular dumplings with white cheese, meat, or vegetable stuffing are called Maultaschen. Savory dumplings made from balls of dough are part of traditional British and Irish cuisine. In Brazil, there are pastels, coxinhas, and bolinhas de carne which are fried dumplings filled with chicken, pork, or beef mixed with olives,
M1060
Journal of Food Science r Vol. 80, Nr. 5, 2015
R C 2015 Institute of Food Technologists
doi: 10.1111/1750-3841.12816 Further reproduction without permission is prohibited
L. monocytogenes in dumplings . . . Table 1–Occurrence of Listeria monocytogenes in dumplings. Contamination with L. monocytogenes [CFU/g]
Type of stuffing in dumplings Meat Vegetablemushroom
White cheese-potato Fruit Total:
Ingredients stuffing Pork and beef, fat, onion, salt, pepper Fermented savoy cabbage, carrot, wild mushrooms, onion, oil, salt, pepper White cheese, potatoes, onion, salt, pepper Strawberries, sugar Blueberries, sugar 9 (A–I)
Number of analyzed producers
Number of analyzed samples
Number of positive samples (% of positive samples before heating)
8 (A–H)
66
6 (A–F)
After cooking in boiling water
Before heating
After microwave heating
35 (53.0)
3 × 102 to 1.4 × 104
0 to 2.7 × 103
03
11
2 (18.2)
5 to 32
nb1
nb1
6 (A–F)
23
4 (17.4)
20 to 80
nb1
nb1
1 (I)
60 40 41 (20.5%)
nb2 nb2 –
nb2 nb2 –
nb2 nb2 0
0 0
200
nb —not analyzed, because the level of contamination reached
