Abstract: The study aimed to evaluate the potential use of spent coffee powder (SCP) and spent tea powder (STP) as bioactive supplements for sponge cake. To achieve this aim, we initially compared the chemical properties of spent tea and coffee powders with those of their raw forms. Subsequently, three supplemented cake blends were prepared (1, 2, and 3% of SCP and STP) to test the effect of their addition on the chemophysical characteristics, sensory attributes, and shelf life of the final products. Our results indicated that spent tea and coffee are prospective materials for polyphenols. Spent tea powder could retain up to 72% (theaflavin trigallate), while spent coffee powder could retain up to 63.9% (1-caffeoylquinic acid) of the identified compounds compared to the raw materials. Furthermore, spent tea and coffee powders contained high levels of dietary fiber (18.95 and 31.65 g/100 g dry weight) and the elements potassium (254.6 and 1218.2 mg/100 g of DW), phosphorus (189.8 and 161.3 mg/100 g of DW), calcium (904.1 and 237.8 mg/100 g of DW), and magnesium (158.8 and 199.6 mg/100 g of DW). In addition, the fortified samples with SCP and STP significantly enhanced the nutritional values while retaining good sensory qualities compared to those of the control sample. Moreover, cakes fortified with the highest concentrations of SCP and STP (3%) showed a significant decrease in malondialdehyde content (MDA; 17.7 and 18.0 μg/g) and microbiological counts (2.4 and 2.5 log cfu/g) compared to the control cake after 14 days of storage. These findings suggest that incorporating SCP and STP into cakes not only enhances their nutritional value but also extends their shelf life. By utilizing these waste products, we can contribute to a more sustainable and ecofriendly food industry.

Introduction

For many years, human development and population growth have been accompanied by the exhaustion and depletion of natural resources and the generation of a significant amount of agri-food waste due to following the linear economy model of “produce, use, then throw away”. (1)

Tea and coffee are the most consumed beverages around the world due to their pleasant aroma, health benefits, and even religious beliefs. (2,3) They are rich in bioactive substances, and their consumption is linked to health benefits, including anti-inflammatory, antioxidant, antiviral, antiallergic, anticancer, and cardiovascular benefits. (4,5) Furthermore, they could enhance memory, mood, and cognitive ability. (6,7)

For both products, around 10% of the dry weight is extracted during brewing in their infusions while around 90% is finally disposed into landfills. (2,8) However, only low molecular weight components are extracted in their respective infusions while the spent coffee powders and tea leaves still retain considerable amounts of bioactive substances, including polyphenols, fibers, and essential elements. (2,9−11)

Currently, the awareness of the general farmers and consumers of terms including sustainable development and circular bioeconomy helped in mitigating this problem, and agri-food waste is now accepted as a valuable resource and re-entered the supply chain via recycling, valorization, energy recovery, and other uses. (2,12−17) In this context, there have been studies on the use of used spent coffee and tea leaves in the field of livestock nutrition, agricultural compost, or production of biogas, or valorized for their bioactive molecules. (2,13,18−21) However, there is a lack of research on the use of spent tea and coffee in the production of novel foods. (22−24)

It has been noted that research on natural functional food additives, including those that exhibit high antioxidant activity, has been developing rapidly in recent years. Consumers prefer antioxidants derived from natural plant sources versus possibly hazardous, manufactured chemicals. (25−28) In this context, several studies have explored the effects of fortifying bakery products with coffee, tea, or their extracts on the technological and nutritional properties of the final products. (29−33) However, to our knowledge, less effort is made to incorporate spent tea or Arabic coffee in making sponge cakes and to investigate their effects on the sensorial, technological, and shelf lives of the final products. Therefore, the current study aimed to (I) evaluate the use of byproducts of tea and Arabic coffee as a novel functional food ingredient in bakery goods; (II) study the impact of adding spent tea or Arabic coffee ground on the sensory qualities, nutritional values, and shelf life of the final product; and (III) validate our findings using chemometric methods. All in all, we aimed to provide normal households with easy-to-use methods to reduce their carbon footprint by utilizing their nutrient-rich food wastes to prepare diverse food concepts to their liking, social habits, and lifestyle.

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Conclusion and Future Perspectives

In conclusion, evaluating spent coffee and tea powders as bioactive supplements for sponge cake showed promising results. Both spent tea and coffee powders were rich sources of bioactive compounds, including polyphenols, and retained high levels of important dietary elements. By incorporation of spent tea and coffee powders into the sponge cake blend, the nutritional value of the cake can be enhanced, providing additional health benefits to consumers. The presence of bioactive compounds in the powders also contributes to the potential antioxidant activity and reduction of peroxide production and delays microbial growth during storage. Finally, further research could explore the potential applications of leftover coffee and tea powders in other food products such as bread or snacks. Additionally, investigating the economic feasibility of large-scale utilization of these waste products would be beneficial in determining their viability for commercial production.