Evaluation of microbial adjuncts and their effect on the ripening of cheddar cheese

A bacteriocin-producing strain of Lactobacillus paracasei DPC 4715 was used as an adjunct culture in Cheddar cheese in order to control the growth of “wild” nonstarter lactic acid bacteria. No suppression of growth of the indicator strain was observed in the experimental cheese. The bacteriocin produced by Lactobacillus paracasei DPC 4715 was sensitive to chymosin and cathepsin D and it may have been cleaved by the rennet used for the cheese manufactured or by indigenous milk proteases. A series of studies were performed using various microbial adjuncts to influence cheese ripening. Microbacterium casei DPC 5281, Corynebacterium casei DPC 5293 and Corynebacterium variabile DPC 5305 were added to the cheesemilk at level of 109 cfu/ml resulting in a final concentration of 108 cfu/g in Cheddar cheese. The strains significantly increased the level of pH 4.6-soluble nitrogen, total free amino acids after 60 and 180 d of ripening and some individual free amino acids after 180 d. Yarrowia lipolytica DPC 6266, Yarrowia lipolytica DPC 6268 and Candida intermedia DPC 6271 were used to accelerate the ripening of Cheddar cheese. Strains were grown in YG broth to a final concentration of 107 cfu/ml, microfluidized, freeze-dried and added to the curd during salting at level of 2% w/w. The yeasts positively affected the primary, secondary proteolysis and lipolysis of cheeses and had aminopeptidase, dipeptidase, esterase and 5’ phosphodiestere activities that contributed to accelerate the ripening and improve the flavor of cheese. Hafia alvei was added to Cheddar cheesemilk at levels of 107 cfu/ml and 108 cfu/ml and its contribution during ripening was evaluated. The strain significantly increased the level of pH 4.6-soluble nitrogen, total free amino-acids, and some individual free amino-acids of Cheddar cheese, whereas no differences in the urea-polyacrylamide gel electrophoresis (urea-PAGE) electrophoretograms of the cheeses were detected. Hafia alvei also significantly increased the level of some biogenic amines. A low-fat Cheddar cheese was made with Bifidobacterium animalis subsp. lactis, strain BB-12® at level of 108 cfu/ml, as a probiotic adjunct culture and Hi-Maize® 260 (resistant high amylose maize starch) at level of 2% and 4% w/v, as a prebiotic fiber which also played the role of fat replacer. Bifidobacterium BB-12 decreased by 1 log cycle after 60 d of ripening and remained steady at level of ~107 cfu/g during ripening. The Young’s modulus also increased proportionally with increasing levels of Hi-maize. Hencky strain at fracture decreased over ripening and increased with increasing in fat replacer. A cheese based medium (CBM) was developed with the purpose of mimicking the cheese environment at an early ripening stage. The strains grown in CBM showed aminopeptidase activity against Gly-, Arg-, Pro- and Phe-p-nitroanalide, whereas, when grown in MRS they were active against all the substrates tested. Both Lb. danicus strains grown in MRS and in CBM had aminotransferase activity towards aromatic amino acids (Phe and Trp) and also branched-chain amino acids (Leu and Val). Esterase activity was expressed against p-nitrophenyl-acetate (C2), pnitrophenyl- butyrate (C4) and p-nitrophenyl-palmitate (C16) and was significantly higher in CBM than in MRS.

Characterisation and application of fruit by-products as novel ingredients in gluten-free products

The physicochemical and nutritional properties of two fruit by-products were initially studied. Apple pomace (AP) contained a high level of fibre and pectin. The isolated AP pectin had a high level of methylation which developed viscous pastes. Orange pomace also had high levels of fibre and pectin, and it was an abundant source of minerals such as potassium and magnesium. Due to the fibrous properties of orange pomace flour, proofing and water addition were studied in a bread formulation. When added at levels greater than 6%, the loaf volume decreased. An optimised formulation and proofing time was derived using the optimisation tool; these consisted of 5.5% orange pomace, 94.6% water inclusion and with 49 minutes proofing. These optimised parameters doubled the total dietary fibre content of the bread compared to the original control. Pasting results showed how orange pomace inclusions reduced the final viscosity of the batter, reducing the occurrence of starch gelatinisation. Rheological properties i.e. the storage modulus (G') and complex modulus (G*) increased in the orange pomace batter compared to the control batter. This demonstrates how the orange pomace as an ingredient improved the robustness of the formulation. Sensory panellists scored the orange pomace bread comparably to the control bread. Milled apple pomace was studied as a potential novel ingredient in an extruded snack. Parameters studied included apple pomace addition, die head temperature and screw speed. As screw speed increased the favourable extrudate characteristics such as radical expansion ratio, porosity and specific volume decreased. The inclusion of apple pomace had a negative effect on extrudate characteristics at levels greater than 8% addition. Including apple pomace reduced the hardness and increased the crispiness of the snack. The optimised and validated formulation and extrusion process contained the following parameters: 7.7% apple pomace, 150°C die head temperature and a screw speed of 69 rpm.