Designing the pH-sensitive indicator based on starch nanoparticle with bromocresol green for monitoring meat spoilage.

The starch nanoparticle, combined with bromocresol green (BCG), served as a pH-sensitive indicator to monitor meat quality throughout an 8-day refrigerated storage period. The meat samples were sealed in package which the pH-sensitive indicator attached to the interior part of packaging lid. The changes in meat quality were evaluated by total volatile base nitrogen (TVBN), pH, total viable count (TVC), sensory analysis, and color in interval of 0, 3, 5, 7, and 8-days storage at 4°C. Initial TVBN values were recorded at 19.6 mg/100 g, increased to 26.6 mg/100 g by the end of storage period. The pH value was significantly increased after 8 days storage at 4°C. The observed color variation in the indicator from yellow to blue was attributed to the concurrent increases in TVBN, TVC, and pH. The indicator color changes had significant correlation with analyzed chemical quality of stored meat. Therefore, the designed BCG pH-sensitive indicator could be effective in monitoring the meat spoilage during storage.

A review on improving the sensitivity and color stability of naturally sourced pH-sensitive indicator films.

Naturally sourced pH-sensitive indicator films are of interest for real-time monitoring of food freshness through color changes because of their safety. Therefore, natural pigments for indicator films are required. However, pigment stability is affected by environmental factors, which can in turn affect the sensitivity and color stability of the pH-sensitive indicator film. First, natural pigments (anthocyanin, betalain, curcumin, alizarin, and shikonin) commonly used in pH-sensitive indicator films are presented. Subsequently, the mechanisms behind the change in pigment color under different pH environments and their applications in monitoring food freshness are also described. Third, influence factors, such as the sources, types, and pH sensitivity of pigments, as well as environmental parameters (light, temperature, humidity, and oxygen) of sensitivity and color stability, are analyzed. Finally, methods for improving the pH-sensitive indicator film are explored, encapsulation of natural pigments, incorporation of a hydrophobic film-forming matrix or function material, and protective layer have been shown to enhance the color stability of indicator films, the addition of copigments or mental ions, blending of different natural pigments, and the utilization of electrospinning have been proved to increase the color sensitivity of indicator films. This review could provide theoretical support for the development of naturally sourced pH-sensitive indicator films with high stability and sensitivity and facilitate the development in the field of monitoring food freshness.

Recent advances in pH-sensitive indicator films based on natural colorants for smart monitoring of food freshness: a review.

As a new type of packaging method, natural pigment-based pH-sensitive indicator film packaging can be used to intelligently monitor food freshness, provide consumers with intuitive food freshness information, and own the advantages of small size, low cost and intuitive accuracy. Based on the introduction of the principle of natural pigment in pH-sensitive indicator film intelligent packaging, this paper reviews the types of natural pigment indicators (such as anthocyanins, curcumin) and film-forming matrix materials, and systematically discusses the research progress of their application in freshness monitoring in various foods, and points out the limitations of this intelligent packaging in practical applications. In order to provide natural pigment in the application and promotion of pH-sensitive indicator film packaging for monitoring food freshness, further research and development works are required to overcome the current limitations. The needs for further research and developments are outlined.

Recent advances in the fabrication of pH-sensitive indicators films and their application for food quality evaluation.

Over a few decades, anthocyanin (ACN)-based colorimetric indicators in intelligent packaging systems have been widely used to monitor the freshness or spoilage of perishable food products. Most of the perishable food products are highly susceptible to enzymatic/microbial spoilage and produce several volatile or nonvolatile organic acid and nitrogenous compounds. As a result, the natural pH of fresh foods significantly changes. Fabrication of CAN-based colorimetric indicators in intelligent packaging systems is an advanced technique that monitors the freshness or spoilage of perishable foods based on the display of color variations at varying pH values. This study focuses on the advancement of pH-sensitive indicators and extraction of colorimetric indicators from commercially available natural sources. Moreover, the fabrication techniques and widespread industrial applications of such indicators have also been discussed. In addition, readers will get information about the color-changing and antioxidant mechanisms of ACN-based indicator films in food packaging.

Clinical testing on SARS-CoV-2 swab samples using reverse-transcription loop-mediated isothermal amplification (RT-LAMP).

BACKGROUND: High cost of commercial RNA extraction kits limits the testing efficiency of SARS-CoV-2. Here, we developed a simple nucleic acid extraction method for the detection of SARS-CoV-2 directly from nasopharyngeal swab samples. METHODS: A pH sensitive dye was used as the end point detection method. The obvious colour changes between positive and negative reactions eliminates the need of other equipment. RESULTS: Clinical testing using 260 samples showed 92.7% sensitivity (95% CI 87.3-96.3%) and 93.6% specificity (95% CI 87.3-97.4%) of RT-LAMP. CONCLUSIONS: The simple RNA extraction method minimizes the need for any extensive laboratory set-up. We suggest combining this simple nucleic acid extraction method and RT-LAMP technology as the point-of care diagnostic tool.

Electrospun fiber mats based on chitosan-carrageenan containing Malva sylvestris anthocyanins: Physic-mechanical, thermal, and barrier properties along with application as intelligent food packaging materials.

This study aimed to encapsulate Malva sylvestris extract (MSE) into chitosan-carrageenan (CH-KC) fibers using the electrospinning technique and monitor the freshness of silver carp fillets during the refrigerated storage conditions for 8 days. The CH-KC + MSE 4 % fiber mats were red at pH values lower than 3, purple at pH 4-6, dark blue at pH 7, green at pH 8-10, and brown at pH 11-12. The tensile strength, elongation at break, water vapor permeability, oxygen transmission rate, moisture content, and water solubility of fabricated fiber mats were 7.71-11.02 MPa, 13.12 %-30.00 %, 7.35-20.01 × 10-4 g mm/m2 h Pa, 3.81-8.23 cm3/m2 h, 15.74 %-27.34 %, and 3.90 %-7.56 %, respectively. Regarding the potential application of a fabricated indicator for freshness monitoring of silver carp fillets, total viable count, psychrotrophic bacterial count, pH, and total volatile basic nitrogen reached 8.91 log CFU/g, 8.03 log CFU/g, 8.10, and 40.18 mg N/100 g at the end of the study, respectively. Meanwhile, the CH-KC + MSE 4 % fiber mat color changed from white to green. These findings suggest that CH-KC + MSE 4 % fiber mats can be further utilized in the food industry to control the freshness of refrigerated silver carp fillets.

A Closed-Tube Loop-Mediated Isothermal Amplification Assay for the Visual Detection of Staphylococcus aureus.

Food-borne diseases induced by Staphylococcus aureus contamination seriously affect human health and food safety. Therefore, a closed-tube loop-mediated isothermal amplification (LAMP) assay for the visual detection of S. aureus was developed in this study. Firstly, two pairs of outer and inner primers were designed targeting on a conserved fragment of gyrB gene in different S. aureus strains. Secondly, the weakly buffered gyrB-LAMP assays were optimized under various pH values and other conditions, followed by the visual evaluation of five pH-sensitive indicators, and the cresol-red was chosen as the best dye for the best visual performance. Thirdly, the cresol-red-based LAMP assay showed good sensitivity with the detection limit of 5.4 copies/µL for purified DNAs, and good specificity with no cross-reaction with other related species. The specificity of the amplified products was further confirmed by XbaI restriction enzyme digestion analysis. Finally, the cresol-red-based LAMP assay was validated by the clinical-dried fish samples inoculated with known numbers of S. aureus and further validated by 20 blind samples. To our knowledge, this is the first report of a closed-tube LAMP assay based on pH-sensitive indicators for the visual detection of the food-borne S. aureus by the gyrB gene.