Unsuspected role of pH in the development of texture and functionalities in Swiss-cheese

The αs1-casein hydrolysis has been shown to greatly influence the texture and techno-functionalities of hard cooked cheeses. This hydrolysis can be performed by the proteinases of the thermophilic lactobacilli since rennet, also implied, is denatured during the cooking step. However, it is unclear whether these changes are only due to the proteolytic activity of lactobacilli, the pH decrease in cheese or both. Small scale Swiss-cheeses were made from microfiltered milk using various combinations of starters including or not lactobacilli: i) Streptoccocus thermophilus alone (STH cheeses), ii), S. thermophilus in enriched lactose cheesemilk (STH-LACT cheeses) to reach pH level similar to cheese with lactobacilli and iii) S. thermophilus and lactobacilli either L helveticus (STH/LH cheeses), or L. delbrueckii subsp lactis (STH/LL cheeses). As S. thermophilus does not metabolize the galactose moiety of lactose, the pH at day 1 of these STH-LACT cheeses was similar to those made with lactobacilli (pH 5.15-5.25) while pH values of the STH cheeses were higher (pH 5.40). Higher firmness and chewiness of the melted ripened STH cheeses were correlated with a higher pH at day 1 and with a lower proteolysis (twofold amount of remaining intact αs1-casein) compared to the STH-LACT cheeses as well as the cheeses with lactobacilli. Conversely, the stretchability showed different behaviors depending both on the quantitative and qualitative proteolysis and on the pH value. The lower pH and content in small peptides led to higher stretchability of the STH-LACT and STH/LH cheeses in contrast to the cheeses STH (high pH and few small peptides) and STH/LL (low pH and high amount of small peptides). In conclusion, the decrease in pH due to the use of lactobacilli plays a key role in the texture of raw and melted Swiss-cheese. Beside the pH, the proteolytic activity of lactobacilli is also a determinant factor for stretchability

Protéases de Lactobacillus helveticus et leurs conséquences sur les propriétés culinaires de l’emmental

Dossier Technique n° 26 d' ACTILAITLactobacillus helveticus possède un équipement protéolytique complexe incluant non seulement une multitude de peptidases intracellulaires bien connues, mais aussi une ou plusieurs protéases de paroi plus méconnues. Quel est l’impact de ces enzymes et de leur biodiversité sur la protéolyse et les propriétés fonctionnelles des fromages à pâte pressée ? C’est l’une des thématiques majeures de l’Unité Mixte de Technologie Caséolis de Rennes. Voici quelques résultats qui illustrent comment les protéases de paroi des lactobacilles peuvent modifier les propriétés filantes des fromages

Protéases de Lactobacillus helveticus et leurs conséquences sur les propriétés culinaires de l’emmental

Dossier Technique n° 26 d' ACTILAITLactobacillus helveticus possède un équipement protéolytique complexe incluant non seulement une multitude de peptidases intracellulaires bien connues, mais aussi une ou plusieurs protéases de paroi plus méconnues. Quel est l’impact de ces enzymes et de leur biodiversité sur la protéolyse et les propriétés fonctionnelles des fromages à pâte pressée ? C’est l’une des thématiques majeures de l’Unité Mixte de Technologie Caséolis de Rennes. Voici quelques résultats qui illustrent comment les protéases de paroi des lactobacilles peuvent modifier les propriétés filantes des fromages

Isovaleric acid is mainly produced by Propionibacterium freudenreichii in Swiss cheese

Isovaleric acid (3-methylbutyric acid) and 2-methylbutyric acid contribute to Swiss cheese flavour. In order to determine the contribution of propionibacteria (PAB) to the production of methylbutyric acids, mini-Swiss cheeses were manufactured with or without PAB as a secondary starter (25 Propionibacterium freudenreichii strains), associated with different cultures of thermophilic lactic starters. In the presence of PAB, the quantity of methylbutyric acids was three to ten times greater, depending on PAB strain, than in the absence of PAB, regardless of the species and the strain of lactobacilli used (20–63 vs. o6mgkg 1 ripened cheese). PAB produced methylbutyric acids concomitantly with acetic and propionic acids, then kept on producing methylbutyric acids after propionic fermentation. The increase in salt-in-moisture content of cheese from 1.0% to 1.8% induced a strain-dependent inhibition of isovaleric acid production. This study shows that P. freudenreichii is the main contributor to methylbutyric acid production in Swiss cheese

A review on functional properties of peptides: from dilute solutions to food products

Pools of peptides have been increasingly used in food formulations due to their particular functional properties such as solubility, gelation or even emulsifying and foaming properties. Peptides, through their physico-chemical and structural characteristics and the generated interactions with one another or other molecules are able to modulate the food texture. Peptide functional properties have been mostly studied in diluted model media and relationships between peptide characteristics and their functionalities have been clearly stated. However, the composition of diluted model media is far from that of food products. Consequently, relationships between peptide characteristics and their functional properties remain enigmatic in complex media, and a fortiori in food. Actually, the composition of peptides in food products still remains hardly unknown. The aim of this review is to show to what extent the relationship between the physico-chemical and structural characteristics of peptides and their functionalities is established. It also focuses on the recent advances made to fill the gaps between model media and food products.We will first report examples in which the relationship is well established and how peptides self-assemble to form supramolecular structures, which are able to modulate the medium texture. Second, we will focus on peptide self-assembly in more complex media, such as « crowded media », which are intermediaries between model media and food products. For food products, the complexity is increased due to the presence of components besides peptides which could interact with peptides and affect the food properties. Several studies have been focused on the degree of hydrolysis of proteins and the texture properties of the food product, without clear relationship between both. Consequently, extrapolation of the results obtained from model media to food products is still hard. Nowadays, through the advances in identification methods of peptides in food products, information on types of peptides present within becomes available. This gives rise a more comprehensive view of the food product and how peptides can modulate food texture. The next steps will be to control (i) how the peptides are produced and interact with the other components and (ii) which quantity of peptides is needed to have optimal functional properties

A review on functional properties of peptides: from dilute solutions to food products

Pools of peptides have been increasingly used in food formulations due to their particular functional properties such as solubility, gelation or even emulsifying and foaming properties. Peptides, through their physico-chemical and structural characteristics and the generated interactions with one another or other molecules are able to modulate the food texture. Peptide functional properties have been mostly studied in diluted model media and relationships between peptide characteristics and their functionalities have been clearly stated. However, the composition of diluted model media is far from that of food products. Consequently, relationships between peptide characteristics and their functional properties remain enigmatic in complex media, and a fortiori in food. Actually, the composition of peptides in food products still remains hardly unknown. The aim of this review is to show to what extent the relationship between the physico-chemical and structural characteristics of peptides and their functionalities is established. It also focuses on the recent advances made to fill the gaps between model media and food products.We will first report examples in which the relationship is well established and how peptides self-assemble to form supramolecular structures, which are able to modulate the medium texture. Second, we will focus on peptide self-assembly in more complex media, such as « crowded media », which are intermediaries between model media and food products. For food products, the complexity is increased due to the presence of components besides peptides which could interact with peptides and affect the food properties. Several studies have been focused on the degree of hydrolysis of proteins and the texture properties of the food product, without clear relationship between both. Consequently, extrapolation of the results obtained from model media to food products is still hard. Nowadays, through the advances in identification methods of peptides in food products, information on types of peptides present within becomes available. This gives rise a more comprehensive view of the food product and how peptides can modulate food texture. The next steps will be to control (i) how the peptides are produced and interact with the other components and (ii) which quantity of peptides is needed to have optimal functional properties

Ethyl ester formation is enhanced by ethanol addition in mini swiss cheese with and without added propionibacteria

Esters are important contributors to cheese flavor, but their mechanisms of synthesis in cheese are largely unknown. This study aimed to determine whether ethanol concentration limits the formation of ethyl esters in cheese. Mini Swiss cheeses were manufactured with (E) or without (C) the addition of ethanol to cheese milk. Ethanol concentrations (enzymatic analysis) were 64 ± 17 and 330 ± 82 g g-1, respectively, in C and E cheeses. E cheeses also contained 5.4 ± 2.3 times more of the five ethyl esters quantified than C cheeses, regardless of the concentrations of esters in C cheeses (range 1-128 ng g-1). Furthermore, the presence of propionibacteria added as acid-producing secondary starters was associated with greater concentrations of esters, due to the increase in acid concentrations that propionibacteria induced and/or to an involvement of propionibacteria enzymes in ester synthesis. This study demonstrates that ethanol is the limiting factor of ethyl ester synthesis in Swiss cheese

Impact de la protéolyse des lactobacilles thermophiles sur les propriétés filantes de l'emmental

Proteolysis is known to be a key factor for cheese stretchability. However, proteolysis in Swiss cheese is rather limited because of the inactivation of rennet during cooking. To determine the contribution of the main agents of Swiss cheese proteolysis, experimental cheeses were manufactured with various Lactobacillus cultures or with various amounts of plasmin added. Marked differences in stretchability were observed among the Lactobacillus cultures. Lactobacillus helveticus strains yielded higher stretchability than Lactobacillus delbrueckii subsp. lactis strains and than mixed cultures of both species. Plasmin addition improved the stretchability at the early stages of ripening (cold room ripening) only. Strong relationships were observed between the proportion of hydrophobic peptides in the fraction of pH 4.6-soluble nitrogen and cheese stretchability. These results show that Lactobacillus culture is a key factor for Swiss cheese stretchability and suggest the involvement of hydrophobic soluble peptides in Swiss cheese stretchability.La protéolyse des fromages joue un rôle déterminant dans leur aptitude à filer à chaud. Dans les fromages à pâte pressée cuite, la protéolyse est cependant limitée en raison de l'inactivation de l'enzyme coagulante pendant l'étape de cuisson. Pour déterminer la contribution des deux principaux agents protéolytiques de l'emmental, des fabrications expérimentales ont été réalisées en mettant en œuvre différentes cultures de lactobacilles thermophiles et différents niveaux d'addition de plasmine dans le lait. De fortes disparités de propriétés filantes ont été observées selon la culture de lactobacille utilisée. Les souches de Lactobacillus helveticus ont conduit à de fortes propriétés filantes comparativement aux souches de Lactobacillus delbrueckiii subsp. lactis ou aux cultures mixtes associant des souches de ces deux espèces. L'addition de plasmine n'a augmenté les propriétés filantes des fromages qu'aux premiers stades de l'affinage (cave froide). Pour ces deux types d'expérimentations, de fortes relations entre la longueur des fils et la proportion de peptides hydrophobes dans l'azote soluble ont pu être établies. Ces résultats montrent que le choix de la culture de lactobacille thermophile est un facteur clef des propriétés filantes de l'emmental. Ils suggèrent également la participation de peptides hydrophobes solubles dans le mécanisme de formation des fils d'emmental fondu

A simple screening methodfor isovaleric acidproduction by Propionibacterium freudenreichii in Swiss cheese

Isovaleric acid (3-methylbutyric acid) and 2-methylbutyric acid are cheese flavour compounds and are produced in Swiss cheese mainly by propionibacteria (PAB), with large variations in amounts depending on the strain. To evaluate the possibility of screening this property in vitro, the production of both acids (referred to as methylbutyric acids) was compared for eight Propionibacterium freudenreichii strains both in mini-Swiss cheeses and in liquid cultures (salted-yeast extract-peptone-lactate medium, pH 5.4, incubated at 24°C then at 6°C). Similar time courses of methylbutyric acid production were observed in cheeses and in liquid cultures. PAB produced methylbutyric acids during propionic fermentation at 24°C (8–37 mg kg−1, and 5–13 mg L−1, respectively, in cheeses and cultures), and during further storage at 6°C for 2 months (11–77 mg kg−1 and 5–17 mg L−1). PAB strains significantly (P<0.05) influenced the amounts produced, and they were similarly classified in cheeses and in liquid cultures. This simple screening method has potential for selection of high- or low-producing strains for cheese manufacture

INTERAKSI SOSIAL MAHASISWA DAN PELAJAR ASRAMA DAYA TAKA PUTRA DENGAN MASYARAKAT JENGGOTAN

Dalam berjalannya waktu kepadatan penduduk di Indonesia semakin padat, dan tidak terkecuali dengan Daerah Istimewa Yogyakarta. Menurut data Dinas Pertanahan dan Tata Ruang DIY adanya peningkatakan dikawasan Permukiman dari 2013 sampai 2015. Terlebih lagi dengan citra kota Yogyakarta yang bergelar sebagai Kota Pelajar menjadi pemikat bagi siswa luar daerah untuk melanjutkan studynya di kota ini. Menjadikan sebuah alasan mendorong Pemerintah Daerah asal siswa untuk memberikan fasilitas yang memadai untuk masa depan pemimpin daerahnya yaitu Asrama. Di balik adanya asrama tentu ada masyarakat sekitar yang sudah terlebih dulu menetap dan menjalankan norma-norma yang berlaku di masyarakat. Tentunya juga bagaimana mahasiswa pendatang ini beradaptasi dengan lingkungan sekitar tersebut. Teori yang digunakan dalam penelitian ini adalah teori Interaksi Sosial menurut Gillin dan Gillin, bahwa ada dua bentuk interaksi bersifat asosiasi dan disosiatif. Penelitian ini menggunakan metode penelitian kualitatif deskriptif. Pengumpulan data dalam penelitian ini menggunakan observasi partisipan, yaitu dimana peneliti terjun langsung kelapangan dan tinggal di asrama beberapa hari untuk melihat interaksi warga asrama dengan masyarakat, wawancara dilakukan untuk mendapatkan informasi dari warga Asrama dan masyarakat sekitar asrama, dan dokumentasi sebagai perolehan data berupa tulisan maupun gambar untuk menambah informasi