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The growth and survival of Listeria monocytogenes in polony preserved with chitosan and rosemary extracts

Wed, 01 Jan 2025 00:00:00 GMT

Title: The growth and survival of Listeria monocytogenes in polony preserved with chitosan and rosemary extracts Authors: Rinquest, Zaa-id Abstract: The ubiquitous nature of Listeria monocytogenes has caused major concerns in the processing of ready-to-eat (RTE) foods. Their ability to thrive in environments such as refrigerated conditions and high salt concentration allows L. monocytogenes to persist in RTE foods. This adaptability leads to its persistence and high resistance to synthetic preservatives used in RTE foods such as sodium nitrite and sorbic acid. These factors in the food chain act as potential drivers for L. monocytogenes contamination of RTE foods and listeriosis. Therefore, this study aimed to investigate and evaluate the growth and survival of L. monocytogenes in polony models preserved with natural preservatives, Chitosan [(1, 4)-2-Amino-2-deoxy-β-D-glucan] and Rosemary (Rosmarinus officinalis L.) extract to inhibit the growth and survival of L. monocytogenes in RTE polonies. Four polony models designated P1 (control sample), P2 (chitosan sample), P3 (rosemary sample), P4 (chitosan and rosemary combination) were developed and investigated at 3 different concentration levels (0.5% g/Kg, 1.0% g/Kg and 2.0% g/Kg) and stored at 4 oC and 10 oC for preservation against coliforms (SANS 4832), yeasts and moulds (SANS 7954), E. coli (SANS 7251), S. aureus (SANS 6888) and L. monocytogenes (SANS 11290). Microbiological tests such as total viable counts (TVC) (SANS 4833), coliforms, yeasts and moulds, E. coli, S. aureus and L. monocytogenes were conducted, and all compared to the standard (control) polony model P1. These microbiological tests were also done to ensure that the models were safe for sensory analysis. The growth and survival of L. monocytogenes was observed and evaluated after injecting 103 log cfu/g of L. monocytogenes into the polony models P2, P3 and P4 preserved with chitosan and rosemary extract compared to the control model P1 preserved with salt (NaCl). The antimicrobial activity of chitosan and rosemary extract assisted with inhibition of S. aureus, E. coli and L. monocytogenes. The mean count (cfu/g) for coliforms, TVC and yeasts and moulds were within the acceptable limit and slightly increased on days 5. Polony models inoculated with 103 log cfu/g of L. monocytogenes indicated a steep decrease from P1 to P2 (p < 0.05), indicating less growth in polony models P2 – P4, thus supporting the hypothesis made in this study. For polony models inoculated with L. monocytogenes at different concentration levels indicated a significance (p < 0.05), indicating that polony models preserved with 1.0% g/Kg showed less growth compared to the models preserved at a 0.5% g/Kg and 2.0% g/Kg concentration. The data obtained for storage temperature indicated that the growth of L. monocytogenes in polony models preserved with chitosan and rosemary extract was higher (p < 0.05) at 10 oC compared to polony models stored at 4 oC. Summarising that storage temperature influence the rate of L. monocytogenes. Little to no growth were found during microbial analysis. Considering Food Safety Management systems (FSMS) polony models used for sensory evaluation were regarded as safe to consume. Sensory analysis showed that the control model P1 and chitosan model P2 were preferred by the participants. In summary, this study found that the use of natural preservatives such as chitosan and rosemary during the production of polony models assisted with the inhibition of L. monocytogenes. This provides alternatives to the synthetic preservatives and helps to promote the production and consumption of polonies preserved with natural preservatives. Description: Thesis (MSc (Food Science and Technology))--Cape Peninsula University of Technology, 2025

Functionality of gum Arabic and sodium alginate on selected properties of Bambara groundnut tofu and its chunks

Wed, 01 Jan 2025 00:00:00 GMT

Title: Functionality of gum Arabic and sodium alginate on selected properties of Bambara groundnut tofu and its chunks Authors: Chipeta, Londiwe Mary Abstract: Bambara groundnut (BGN) (Vigna subterranea [L.] Verdc.) is a source of protein (15-25%), making this legume a suitable alternative to soybean for tofu production. The use of BGN as a main ingredient in tofu is not documented, as most tofu is made from soy milk extracted from soaked soybeans. The texture (Instron texture analyser), colour (HunterLab ColorFlex spectrophotometer), rheology (rheometer), proximate (AOAC methods) and microstructure (scanning electron microscope) of BGN tofu as affected by coagulants (vinegar, lemon juice and gluconolactone (GDL)) and hydrocolloids (gum Arabic and sodium alginate) were established in this study. Factorial design and response surface methodology were used to optimise gum Arabic and sodium alginate concentrations at 0.3, 0.4 and 0.5%. The interaction of gum Arabic and sodium alginate was optimal at 0.5%. The combination of gum Arabic and sodium alginate significantly (p < 0.05) increased the hardness (9.15%) and springiness (11.46%) of tofu and decreased its gumminess (19.72%). The lightness of BGN tofu increased as GDL concentration increased. The coefficient of determination (R2 ) for all measurements using the Power law was >0.9. The consistency coefficient (K) of BGN milk extract prepared using GDL with gum Arabic and sodium alginate was >1, indicating shear thickening behaviour. The entrapped water content of BGN tofu ranged from 45.13 (1% GDL-tofu) to 65.60% (0.6% GDL-tofu + 0.5% GA + 0.5% SA). Adding gum Arabic and sodium alginate to BGN tofu increased the protein, ash and carbohydrate content and decreased the moisture content. Vinegar-tofu exhibited a uniform, smaller particle size network and smooth surface. Gum Arabic and sodium alginate had a significant (p < 0.05) positive effect on the functional and sensory qualities of BGN tofu chunks. Leucine (4.34-4.94%) and phenylalanine (4.61-5.62%) were the most abundant essential amino acids in all BGN tofu chunks samples. There was an increase in the protein content of BGN tofu when gum Arabic and sodium alginate ratio was incorporated. Bambara groundnut tofu chunks with 0.6% GDL with gum Arabic and sodium alginate received the highest in appearance, colour, taste, texture and overall acceptability than tofu chunks coagulated with vinegar and 0.6% GDL. The results of this study highlighted the potential of BGN tofu and its chunks as a nutritious, cholesterol-free protein alternative, with the quality and acceptability influenced by coagulant types and hydrocolloid concentrations. Description: Thesis (MSc (Food Science and Technology))--Cape Peninsula University of Technology, 2025

Rheological and stability properties of Citrullus lanatus mucosospermus, lanatus citroides and moringa oleifera seed hydrocolloids in oil-in-water

Wed, 01 Jan 2025 00:00:00 GMT

Title: Rheological and stability properties of Citrullus lanatus mucosospermus, lanatus citroides and moringa oleifera seed hydrocolloids in oil-in-water Authors: Olubi, Olakunbi Abstract: When mixed with water, hydrocolloids create gel-like structures and have grown in popularity due to their wide range of applications in food, medicine, and other industries. The extraction of hydrocolloids from natural sources, such as seeds, is an exciting idea because of the potential diversity in composition and function. In a variety of sectors, the use of seeds from Citrullus lanatus mucosospermus (egusi, EG), Citrullus lanatus citroides (makataan, MA), and Moringa oleifera (moringa, MO) as a hydrocolloid is in line with the growing demand for sustainable and natural products worldwide. This study examined hydrocolloids derived from EG, MA, and MO seeds, highlighting their diverse physicochemical and functional properties. Hydrocolloids were extracted from the seeds and analysed for their proximate composition, particle size distribution, and interfacial tension using the hot water extraction method. The raw oilseed flours had varying amounts of protein. Hydrocolloids had a higher protein concentration than raw oilseeds, greatly improving the amino acid profile. Furthermore, the hydrocolloid ash concentration ranged from 4.09% to 6.52% w/w dry weight, accompanied by low-fat levels. Smaller particles in all hydrocolloid samples showed a more narrow and uniform size distribution, suggesting a better degree of homogeneity in particle size within this range, according to the examination of particle size distribution. This implies a lower chance of size variation for small particles, which may affect their rheological and functional characteristics in different applications. This study also investigated the rheological behaviour of three novel hydrocolloids: egusi seed hydrocolloid (EGH), makataan seed hydrocolloid (MAH), and moringa seed hydrocolloid (MOH) in semi-concentrated (20-50 wt) as well as concentrated (50-75 wt%) slurries, when subjected to a shear steady flow, to reversible minor strain in amplitude as well as frequency sweep modes deformation. The high protein content of these hydrocolloids (48.12%, 34.00%, and 35.00% for MOH, MAH, and EGH, respectively—reduced the interfacial tension. Regardless of the hydrocolloid type and process parameters (pH = 4– 9; temperatures =30-75 oC; mixing time = 1–10 minutes; concentration = 20–50 wt%), semi concentrated slurries were pseudoplastic materials that behave like viscous liquids with no yield stress; G” > G’ in the entire range of strain (0.1–200%). The storage modulus, yield stress, and slurry concentration correlation showed two deflection points/transitional points, 50 wt% and 67 wt%, respectively. The first transition point was present in all three hydrocolloids, whereas the second was only related to EGH and MAH slurries; MOH-based slurries did not display such a point. The first transition point (50 wt%) was associated with the onset of structure formation. The bottle test further confirmed that slurries containing more than 50% by mass hydrocolloids did not flow when inverting the vessels. The second transitional point marked the boundary between the region of the slow or rapid response of the strength or rigidity of the structure of the slurry of EGH and MAH with changes in hydrocolloid concentration. The strength of the structure increased rapidly with the hydrocolloid concentration below this point, whereas a slow increase was observed above the critical point. Conversely, the rigidity of the structure of the slurries displayed an opposite effect. Interestingly, because of its high content of hydrophobic proteins, the dominating mechanism of structure formation within MOH slurries was the entanglement network of polymers (proteins and polysaccharides) whose yield stress originated from the presence of high concentrations of dispersed particulate material within the structure. This gave rise to a weak, predominantly elastic rather than viscous gel with a cohesive energy range of 0.2 – 0.7 kJ. On the other hand, due to their high hydrophilic protein content, the dominant mechanism of structure formation within EGH and MAH slurries could be cross-liking rather than entanglement. This cross linking generated a predominantly elastic gel with a relatively high cohesive energy of 2-7 kJ. The effects of extracted hydrocolloid on the stability and rheological behaviours of oil in-water (O/W) emulsions (MOH, MAH, and EGH) were investigated using plant-based emulsifiers from moringa, makataan, and egusi hydrocolloids. In this work, the mixture design was optimised for each level of limitation between hydrocolloid, oil, and water. Stability testing was used to experiment with and optimise the mixture. The droplet size distributions, morphology, creaming index, and polydispersity index were all measured on 11 emulsions, and the best emulsion with a stable profile was chosen for further investigation. The rheological characteristics and the microscopic morphology were acquired to understand the mechanism and interaction of droplets in the O/W emulsion. The results indicated that optimal for O/W emulsions was found in samples with 20-30% hydrocolloid, 37-40 % oil and 25-45 % water while using the three hydrocolloids. EGH and MAH, with the lowest hydrocolloid composition, showed the smallest droplet size and highest creaming index values. The study concludes by highlighting the promising potential of hydrocolloids generated from egusi (EG), makataan (MA), and moringa (MO) seeds. These plant-based hydrocolloids displayed different functional features, including increased protein content, considerable rheological behaviour, and excellent stabilisation in oil-water emulsions. Their capacity to produce gel-like structures, lower interfacial tension, and increase structural rigidity is useful in food systems, particularly for thickening, emulsifying, and texture modification. These findings add to the growing interest in using sustainable, natural ingredients to improve food formulation and product durability. Description: Thesis (Doctor: Food Science & Technology)--Cape Peninsula University of Technology, 2026

A survey of propionic acid bacteria and the optimisation of vitamin B12 in motoho, an African beverage

Mon, 01 Jan 2024 00:00:00 GMT

Title: A survey of propionic acid bacteria and the optimisation of vitamin B12 in motoho, an African beverage Authors: Nyenye, Letlotlo Abstract: Cereal-based fermentation is an extensive, common and popular practice across the African continent. The variety of fermented food products and beverages produced by means of sorghum fermenting is testament to the practice. Motoho is a sour, porridge-like snack beverage made from brown or red sorghum. Motoho is produced by means of spontaneous fermentation by back slopping with tomoso (starter culture). Lactic acid bacteria (LAB) are reported to be the most dominant microorganisms in spontaneous cereal fermentation, followed by yeasts. Vitamin B12 (vit B12) deficiency is reported to have negative health effects, and therefore, fortification by means of cereal fermentation with Generally Recognised as Safe Organisms (GRAS) has been proposed as a method for addressing vitamin deficiencies. The vitamin content of motoho, especially vit B12 is unknown. Propionibacterium freudenreichii. P. freudenreichii biosynthesises vit B12 naturally and has GRAS status. The aim of this study was to isolate Propionibacterium spp. present in motoho, and optimise the production of vit B12 by means of co-inoculating tomoso with P. freudenreichii subsp shermanii (PAB-J17) at low and high concentrations. The traditional method (back-slopping with tomoso) being utilised as the control. Motoho was prepared using two methods: (i) the traditional method (TFM) (back-slopping with tomoso) and (ii) by co-inoculating tomoso with P. freudenreichii (PABJ-17) in a low (LPAB-J17) and high (HPAB-J17) cell concentrations, respectively. Fermentation was facilitated at 32 °C for 12 h with sampling performed every 3 h. The pH was monitored and the following organisms were enumerated: Total Bacterial Counts, coliforms, lactic acid bacteria (LAB), yeasts and moulds. LAB were the most dominant organisms during the whole fermentation process, with cell counts obtained for TFM being significantly higher (p ≤ 0.05) than LPAB-J17 and HPAB-J17. For total coliform counts, there was no significant difference (p ≥ 0.05) between LPAB-J17 and HPAB-J17. After 12 h of fermentation, there was no yeast growth for TFM. HPAB-J17 obtained the lowest final pH (3.6) after fermentation, with TFM and LPAB-J17 obtaining the same final pH of 4.75. Isolate MFS1 was isolated from MFS by pre-enrichment in Yel-broth (30 °C for 5 d) and sub-culturing on Yel-agar (30 °C for 7 d anaerobically). Isolate MFS1 was Gram-positive with an endospore. The NCBI BLAST resulted in 99.5 % similarity with seven strains. It had 99.5% similarity to the type species of Bacillus rugosus sp. nov. B. rugosus is an emerging organism of the Bacillus genus. MFS1 formed a relatively stable phylogeny at 68 %; the cluster was located in a clade that was 99 % stable. The optimisation of vit B12 was accomplished by co-inoculating tomoso, which was back-slopped with PAB-J17 in a low cell inoculum of 1 × 104 cfu.g-1 (LPAB-J17) and a high cell inoculum of 1 × 108 cfu.g-1 (HPAB-J17). The traditionally fermented motoho (TFM), which was the control obtained a significantly higher (p ≤ 0.05) vit B12 concentration than LPAB-J17; LPAB-J17 vit B12 concentration was significantly (p ≤ 0.05) lower than TFM and HPAB-J17. Inoculum optimisation was successful for HPAB-J17, obtaining vit B12 which was 2-fold higher than the control (TFM) and 5-fold higher than LPAB-J17. Description: Thesis (MSc (Food Science and Technology))--Cape Peninsula University of Technology, 2024