Microbial composition of sweetness-enhanced yoghurt during fermentation and storage

Abstract

The reformulation of dairy products to contain less added sugar can contribute to reducing sugar consumption, thereby reducing the risk of non-communicable diseases. The objective of this study was to investigate the microbial ecology of reformulated yoghurt, which was produced using bi-enzymatic modification of lactose to increase its sweetness by a factor of 2–3. Ultimately, this reformulation strategy could reduce the amount of added sugar needed for equal sweetness of the end product. The bi-enzymatic modification relied on utilisation of a β-galactosidase enzyme to convert the milk sugar lactose to galactose and glucose, followed by the enzymatic conversion of the glucose moiety to fructose using a glucose isomerase. The microbial ecology of reformulated yoghurt produced with two mixed starter culture preparations containing either Streptococcus ( S .) thermophilus and Lactobacillus ( Lb .) delbrueckii or S. thermophilus , Lb. acidophilus and Bifidobacterium sp. strains, was analysed during fermentation and cool storage using 16S rRNA based metagenomics. None of the yoghurt samples showed a significant difference in microbial composition between sweetness-enhanced and regular milk at all sampling time points during manufacture and storage of yoghurt. However, a significant difference between the microbiota of inoculated milk before and after fermentation was observed. In both types of yoghurt, the starter culture genera dominated the microbial ecology at the end of fermentation as expected, reducing the possibility of growth of potentially pathogenic or spoilage bacteria possibly resulting from a changed carbohydrate spectrum.

Effect of reduction of sodium content on the microbial ecology of Edam cheese samples

“…For isolation of genomic DNA, the method published by Luzzi et al ( 2020 ) was modified to suit DNA isolation from inoculated milk, curd and cheese samples. For this, the pelleted samples were defrosted at ambient temperature and resuspended in 1 mL of the lysis buffer used by Luzzi et al ( 2020 ).…”

“…For isolation of genomic DNA, the method published by Luzzi et al ( 2020 ) was modified to suit DNA isolation from inoculated milk, curd and cheese samples. For this, the pelleted samples were defrosted at ambient temperature and resuspended in 1 mL of the lysis buffer used by Luzzi et al ( 2020 ). Next, to each sample 0.4 g of sterile 0.1 mm Zirconium/glass-beads ® (Carl Roth, Karlsruhe, Germany) were added and samples were homogenised for 5–10 min at 80 rpm using an Intelli-Mixer RM-2 M (ELMI, Calabasas, CA, USA) bead-beater set at the U2-mode until homogenous.…”

“…Samples were then further processed using the QIAamp DNA Stool Mini Kit (QIAGEN GmbH, Hilden, Germany) according to the protocol outlined by Luzzi et al ( 2020 ). Briefly, the RNA was first digested using 4 μL of a 10 mg/mL DNAse-free RNase solution (VWR International GmbH, Darmstadt, Germany), after which the proteins were degraded with 30 μL of 20 mg/mL proteinase K solution (AppliChem GmbH, Darmstadt, Germany).…”

“…Briefly, the RNA was first digested using 4 μL of a 10 mg/mL DNAse-free RNase solution (VWR International GmbH, Darmstadt, Germany), after which the proteins were degraded with 30 μL of 20 mg/mL proteinase K solution (AppliChem GmbH, Darmstadt, Germany). The QIAGEN kit’s ‘AL Buffer’ was then added to each sample prior to usage of the QIAamp spin columns to capture and wash the DNA as documented by Luzzi et al ( 2020 ). The concentration of genomic DNA from samples was determined with a Qubit ® 3.0 Fluorometer and the Qubit™ dsDNA BR Assay Kit following the kit specifications (Thermo Fisher Scientific, Darmstadt, Germany).…”

“…The bacterial composition of inoculated milk and cheese samples was assessed using 16S rDNA amplicon sequencing with an Illumina MiSeq™ sequencer (Illumina Inc., San Diego, CA, USA). Library preparation and sequencing was performed according to Luzzi et al ( 2020 ), using the primers targeting the 16S rRNA gene V3 and V4 regions used by these authors.…”