IN Brief:
- FoodUPV researchers tested 16 microwave pretreatment settings before hot-air drying leek-processing residues.
- Moderate pretreatment improved laboratory water-holding capacity by up to 17% and water retention by up to 13%.
- The study does not establish commercial throughput, product performance or a net energy saving for the complete process.
Universitat Politècnica de València researchers have tested microwave pretreatment before hot-air drying to convert leek-processing residues into powdered ingredients, finding that moderate treatment can improve selected water-binding characteristics under laboratory conditions.
The work was published in Applied Sciences on 9 October by Claudia Bas-Bellver, Cristina Barrera and Lucía Seguí of the university’s FoodUPV institute. It examines moisture removal, particle size, antioxidant characteristics and hydration behaviour, rather than reporting an industrial installation or the launch of a commercial food ingredient.
Residues supplied by the Agrícola Villena cooperative in Alicante consisted mainly of green leek leaves. After sanitising, rinsing and grinding the material, the researchers tested 16 combinations of microwave intensity and exposure time. Power settings of 2, 4, 6 and 9 watts per gram were combined with treatments lasting two, four, six or eight minutes to establish the response of the wet vegetable material.
Four-minute pretreatments were then selected for comparison with untreated material during hot-air drying. The samples were exposed to air at 70°C travelling at approximately two metres per second, with a common ten-hour drying treatment used to characterise the final powders. The experimental batches were small; the study used approximately 50-gram portions during microwave screening, rather than a continuous commercial dryer.
Powders produced after pretreatment at 2–4 watts per gram showed improvements in certain hydration measurements. Water-holding capacity rose by as much as 17%, and water-retention capacity by up to 13%, relative to the untreated material. The reported final moisture values at these moderate settings were around 0.5–0.6%, compared with 1.7% for the untreated control.
The results did not follow a simple relationship in which higher microwave power always improved performance. Powder treated at 9 watts per gram reached an even lower measured final moisture content in one comparison, but higher settings generally produced finer particles and poorer wettability. Selecting a condition therefore involves the physical behaviour of the powder as well as its remaining water content.
Microwave energy interacts with water and other polar molecules within the wet plant material, generating heat before the product enters the convective dryer. Hot air then carries away moisture from the exposed material. The treatment can alter tissue structure and the rate at which water moves, but its effect depends on the structure of the plant residues and the amount of water already removed before air drying begins.
Pretreatment changed the amount of water entering the hot-air stage. The microwave-treated material began that stage with a lower and variable initial moisture content, so a change in subsequent drying rate or time cannot by itself demonstrate an improvement in energy efficiency across both operations. The published paper does not provide a validated energy balance for an integrated production line, and no commercial energy saving can be claimed from the laboratory data.
Other measured properties would affect how the powder behaves in food preparation. Wettability describes how quickly dry particles become fully wetted when introduced into water, whereas water-holding capacity measures the amount retained after hydration. Water retention after centrifugation was assessed separately. A powder may absorb a substantial volume of water once hydrated and still be difficult to disperse initially, particularly if a finer particle fraction tends to form clumps.
Particle size became smaller as microwave intensity increased, while the physical volume occupied by a measured mass of powder varied across treatment conditions. These changes could alter dispensing, blending and hydration during subsequent food production. They would need to be tested in a specific food matrix before any claim about improved texture or shorter preparation time could be supported.
Antioxidant characteristics also changed with treatment. Although selected measures increased during parts of the drying process, untreated powders produced the highest final antioxidant values in some comparisons. The researchers measured phenolic compounds and laboratory radical-scavenging activity; those assays do not establish a nutritional or health benefit in a finished product.
Infrared spectroscopy indicated changes in the structure of the dried plant material without major alteration to its principal detectable functional groups. The results suggest that pretreatment affects the physical organisation of the residue, but do not identify a single mechanism responsible for every difference in hydration and antioxidant behaviour.
Leek-derived powders may eventually be assessed for savoury foods, soups, sauces or bakery applications, where fibre and water interaction can influence texture and processing. Neither sensory acceptability nor stability during commercial storage was demonstrated in the research. Microbiological safety, ingredient specification and performance through mixing and cooking would also need validation for individual products.
Industrial adoption would require continuous handling of variable incoming residues, a suitable microwave treatment system, controlled drying and reliable milling. Differences in incoming material moisture and fibre structure could alter how the process performs outside the laboratory. The study establishes measurable changes in powder functionality at moderate microwave settings, while leaving equipment scale, total energy consumption, product acceptance and production economics unresolved.
