Inledning En tredjedel av den mat som produceras i världen slängs (United Nations Development Programme [UNDP], 2020) och de livsmedelsförstörande mikroorganismerna är ett vanligt förekommande problem och en bidragande orsak till det globala matsvinnet (Snyder & Worobo, 2018). Livsmedelsindustrin använder därför olika hurdletekniker för att minimera risken för tillväxt av förskämningsorganismer (Snyder & Worobo, 2018). En strategi för att kontrollera om olika hurdletekniker uppfyller sitt syfte är att utsätta ett livsmedel för ett belastningstest. Syfte Syftet med studien var att genom ett belastningstest i ett flytande livsmedel jämföra konserveringsmedlen lingonjuice och kaliumsorbat + natriumbensoat samt att undersöka produktens fysikaliska och kemiska förändringar över tid.  Material och metod Ett flytande livsmedel (n = 73 á 180 ml) inokulerades i ett belastningstest med log 2–3 mikroorganismer per ml livsmedel. Därefter tillsattes konserveringsmedlen lingonjuice (n = 24) eller kaliumsorbat + natriumbensoat (n = 25). En tredjedel av proverna (n = 24) lämnades utan konserveringsmedel. Provtagning för analys av tillväxt, färg, pH och viskositet (mPas) utfördes vid 0, 14 och 30 dagar efter livsmedlet inokulerats med mikroorganismer.   Resultat Resultatet visade mikrobiell tillväxt i samtliga livsmedel vid dag 0. Dag 14 identifierades tillväxt i livsmedlet med kaliumsorbat + natriumbensoat samt lingonjuice. Vid analysen på dag 30 identifierades tillväxt i livsmedlet med kaliumsorbat + natriumbensoat och i livsmedlet utan konserveringsmedel. Över tiden skedde även fysikaliska förändringar i viskositet och kemiska förändringar av pH-värdet. Gällande färg skedde enbart marginella förändringar. Slutsats Resultatet av belastningstestet visade att lingonjuice är det konserveringsmedel som har bäst effekt med avseende på produktstabilitet genom att hämma tillväxt av tillsatta mikroorganismer. Resultaten av de fysikaliska mätningarna visade på förändringar över tid med avseende på viskositet. Färg visade enbart minimala förändringar. Resultatet av den kemiska mätningen visade på förändringar av pH-värdet över tid. / Introduction One third of food produced in the world is discarded (United Nations Development Program [UNDP], 2020) and food-destroying microorganisms are a common problem and a contributing cause of global food waste (Snyder & Worobo, 2018). The food industry therefore uses various hurdle techniques to minimize the risk of growth of spoilage organisms (Snyder & Worobo, 2018). One strategy to check whether different hurdle techniques meet their purpose is to expose foods in a challenge test. Aim The aim of the study was to compare the preservatives lingonberry juice and potassium sorbate + sodium benzoate and examine any physical and chemical changes over time through a challenge test on a liquid food product. Material and method A liquid food (n = 73 á 180 ml) was inoculated in a challenge test with log 2-3 microorganisms per ml food. Thereafter preservatives lingonberry juice (n = 24) or potassium sorbate + sodium benzoate (n = 25) were added. One third of the samples (n = 24) were left without preservatives. Sampling for analysis of growth, color, pH and viscosity (mPas) was performed at 0, 14 and 30 days after the food was inoculated with microorganisms. Results The results showed microbiological growth in all food products at day 0. Day 14 growth were found in the food with potassium sorbate + sodium benzoate and lingonberry juice. By the analysis on day 30 growth in the food with potassium sorbate + sodium benzoate and in the food without preservatives were showed. Over time physical changes of viscosity and chemical changes of pH occurred. Regard to color only marginal changes occurred. Conclusion The result of the challenge test showed that lingonberry juice is the preservative that has the best effect regard to product stability through inhibiting the added microorganisms. The results of the physical measurements showed changes regard to viscosity over time. Color only showed marginal changes. The result of the chemical measurement showed changes of pH over time.

<p>Microbes play key roles in processes that shape the world around us having direct impact in crop  production,  food  safety,  digestion,  and  overall  health.  Developing  tools  to  monitor  their activity in-situ is the key towards better understanding the true impact of microbial activity in these processes and, eventually, harnessing their potential. Many conventional techniques for microbial activity assessment require sample collection, expensive benchtop equipment, skilled technicians, and   destructive   sample   processing   which   makes   their   adaptation   for   in-situ   monitoring cumbersome. The need for technologies for in-situ monitoring has led to the development of many sensordesigns,  capable  of  detecting  single  strains  of  bacteria  to  low  limits  of  detection  (LOD). These designs, however, are limited to their complex manufacturing procedures, cost, and delicacy which makes them difficult to implement outside of a laboratory setting into harsh environments.</p> <p>In  the  last  25  years,  impedimetric  sensing  methods  have  been used  as  powerful  analytical tools  to  characterize  the  degradation  and  dissolution  of  polymers.  Known  for  their  robustness, these techniqueswere mainly used for characterizing polymer’s properties as corrosion-protective layers on metals. At the time, someresearchers pondered onthe potential use of this technique for biosensing  applications.In  this  thesis,  the  ability  of  monitoring  microbial  activity  in-situ  was explored by  integratingdifferent  bioresponsive  polymers  with  low-cost electronic  impedimetricplatformsand assessing their degradation kinetics in response to microbes</p> <p>This  novel  use  of  impedimetric  sensing  methods  and  approach  towards  microbial  activity sensing was systematically studied in different  areas including  agriculture, food packaging, and healthcare.  Microbes,  the  good,  the  bad,  and  the  ugly,  were  studied  within  their  ecosystems  to demonstrate  the  ability  of  using  the  described  systems  in  in-situ  monitoring.  In  agriculture, polymer  degradation  was  successfully  correlated  to  the  concentration  of  decomposing  bacteria directly in soil. In food packaging, spoilage of chicken samples was successfully detected within their package through a non-reversible system. In healthcare, a wireless and electronic-free wound monitoring  system  capable of  detecting  early  onset  of  infection  while  delivering  therapeutics without the need of external actuation was achieved. Further developments of this technology will present the key towards monitoring microbial activity in-situ in a large scale, providing solutions to  humanity’s  toughest  upcoming  challenges  including  food  production,  food  safety,  and healthcare.</p>

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Traditional fabrication methods used to manufacture biosensors for physiological, therapeutics, or health monitoring purposes are complex and rely on costly materials, which has hindered their adoption as single-use medical devices. The development of a new kind of wearable and implantable electronics relying on inexpensive materials for their manufacturing will pave the way towards the ubiquitous adoption of sticker-like health tracking devices.<div>One of growing and most promising applications for biosensors is the continuous health monitoring using mechanically soft, stretchable sensors. While these healthcare devices showed an excellent compatibility with human tissues, they still need highly trained personnel to perform multi-step, prolonged fabrication for several functioning layers of the device. In this dissertation, I propose low-cost, scalable, simple, and rapid manufacturing techniques to fabricate multifunctional epidermal and implantable sensors to monitor a range of biosignals including heart, muscle, or eye activity to characterizing of biofuids such as sweat. I have also used these devices as an implant to provide heat therapy for muscle regeneration and optical stimulation of neurons using optogenetics. These devices have also combined with those of triboelectric<br>nanogenerators to realize self-powered sensors for monitoring imperceptible mechanical biosignals such as respiratory and pulse rate.</div><div>Food health and safety has also emerged as another important frontier to develop biosensors and improve the human health and quality of life. The recent progresses on detecting microbial activity inside foods or their packages rely on development of highly functional materials. The existing materials for fabrication of food sensors, however,<br>are often costly and toxic for human health or the environment. In this dissertation, I proposed biocompatible food sensors using protein/PCL microfibers to reinforce the protein microfibrous structure in humid conditions and exploit their excellent hygroscopic properties to sense biogenic gas, as an indicator for early detection of food spoilage. Finally, my battery-free food sensors are capable of monitoring food safety with no need of extra measurement devices. Collectively, this dissertation proposes cost-effective solutions to solve human health issues, enabled by developing low-cost, functional materials and exploiting simple fabrication techniques.<br></div>